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LIVING  PLANTS  AND  THEIR 
PROPERTIES 


PLANT  OF  WILD  LETTUCE 
The  left  hand  figure  as  seen  from  the  east,  the  other  figure  as 
seen  from  the  south,  showing  the  compass-like  habit  of  adjust- 
ing the  leaves  in  the  meridional  plane. 


LIVING  PLANTS  AND  THEIR 
PROPERTIES 


A  COLLECTION  OF  ESSAYS 


JOSEPH  CHARLES  ARTHUR  Sc.  I). 

PROFESSOR  OF  VEGETABLE  PHYSIOLOGY  AND   JATHOLOGY 
IN  PURDUE  UNIVERSITY 


DANIEL  TREMBLY  MAC  DOUGAL  Ph.  D. 

ASSISTANT  PROFESSOR  OF  BOTANY  IN  CHARGE  OF  PLANT 
PHYSIOLOGY  IN  THE  UNIVERSITY  OF  MINNESOTA 


NEW  YORK 

BAKER  AND  TAYLOR 

MINNEAPOLIS:  MORRIS  AND  WILSON 
1898 


COPYRIGHT  BY 
J.  C.  ARTHUR  AND  D.  T.  MAC  DOUGAL 

1898 


UNIVERSITV  PRESS  OK  MINNESOTA 
MINNEAPOLIS 


PREFACE 

The  essays  comprised  in  this  book  are  selected  from 
popular  addresses  and  articles  presented  by  the  authors 
within  the  last  five  years.  The  unequal  conditions  of 
the  original  preparation  have  made  it  necessary  to  revise 
and  rewrite  certain  articles  in  order  to  meet  the  require- 
ments of  their  juxtaposed  position.  The  occasion  has 
been  seized  to  omit  portions  less  relevant  in  the  present 
connection,  and  to  amplify  others  to  meet  the  demands 
of  continuity,  clearness,  and  harmony  with  current  bo- 
tanical thought.  The  original  presentation  of  each  sul)- 
ject  is  denoted  by  a  foot-note  under  the  title.  The  au- 
thors are  separately  responsible  for  the  chapters  to 
which  their  names  are  signed  in  the  table  of  contents. 

The  publication  of  this  volume,  it  is  believed,  is  justi- 
fied by  the  appreciation  accorded  the  essays,  upon 
their  first  appearance;  and  it  is  the  hope  of  the  authors 
that  it  may  stimulate  an  interest  in  the  phases  of  botany 
covered,  both  among  general  readers  and  also  among 
workers  in  the  co-ordinate  branches  of  animal  biology. 
March,  1898.  The  Authors. 


n 


TABLE  OF  CONTENTS 

I.  The  Special  Senses  of  Plants,  J.  C.  Arthur 1 

Eighteenth  century  opinions — Application  of  terms — 
Knowledge  of  mechanism— Primary  unity  with  great  di- 
versity— What  constitute  special  senses — Sense  of  con- 
tact— Trend  of  sense  development — Free  and  fixed  organ- 
isms— Discovery  of  gravity  sense — Movement  connected 
with  growth — Transmission  of  impulses — Sensitiveness 
to  light — Chemical  sense— Moisture  sense. 

II.  The  Development  of  Irritability,  D.  T.  Mac- 

DOUGAL 19 

Derivationof  existing  forms— Chlorophyll  and  sunlight — 
Pollination— Organization  of  shoot — Distribution  of  nu- 
tritive factors — Sensory  and  motor  zones — Development 
of  root  functions — Nutritive  factors  in  soil— Organization 
of  roots. 

III.  Wild  Lettuce  as  Weed  and  Compass  Plant,  J. 

C.  Arthur 31 

Likeness  to  cultivated  lettuce — General  characters  and 
habit — First  appearance  in  America — Fifteen  years  of  con- 
quest— Seeds  and  their  distribution — How  to  be  a  success- 
ful weed — Even  a  weed  may  be  interesting — The  habit  of 
polarity— Another  compass  plant— Explanation  of  the 
peculiar  trait. 


vin  LIVING   PLANTS 

IV.  Mimosa  :  A  Typical  Sensitive  Plant,  D.  T.  Mac- 

DOUGAL 47 

ITses  of  movement — Power  of  movement— Characteristics 
of  mimosa — Organization— Day  position  of  leaves — Night 
position  of  Leaves — Reaction  to  shock,  etc. — Transmis- 
sion of  stimuli — Repetition  of  stimuli — Methods  of  trans- 
mission— Purpose  of  reaction  to  shock. 

V.  Universality  of  Consciousness  and  Pain,  J.  C. 

Arthur 63 

Unity  in  nature — Superstition  of  the  mandrake — Can 
a  mandrake  feel — Meaning  of  consciousness — Examples 
of  consciousness — Definition  of  terms — General  irritabil- 
ity—Welfare of  the  organism— Adaptive  movements  im- 
ply consciousness — Pain  a  factor  in  evolution — Action  of 
plants  difficult  to  interpret — Plants  not  degenerates. 

VI.  How  Cold  Affects  Plants,  D.T.MacDougal.  85 

Varying  reaction  to  cold — Appearance  of  frozen  plants — 
Ice  in  the  tissues — Relation  of  cell  to  cold— Relation  of 
organism  to  cold — Death  above  freezing  point — Adapta- 
tions against  cold. 

VII.  Two  Opposing  Factors  of  Increase,  J.  C.  Ar- 

thur   99 

Two  sides  to  plants — Nutrition  and  development — Eflect 
of  soil  fertility— Provision  for  perpetuit3'— Size  of  seeds — 
Early  growth — Final  yield — Superiority  of  large  seeds — 
Vegetative  and  fruiting  parts  compared — External  and 
internal  factors. 

VIII.  ChlorophyllandGrowth,  D.T.MacDougal.  121 

Historical — Methods  of  experimentation — Growth  in  the 
absence  of  carbon  dioxide — Eflect  of  darkness — Total  re- 
sults with  Arisrema — Results  with  Calla — Results  with 
Zea — Results  with  Phoenix — Ordinary  course  of  growth 
— Growth  with  insufficient  nutrition — Conclusions 

IX.  Leaves  in  Spring,  Summer,  and  Autumn,    D.  T. 

MacDougal 145 

Importance  of  chlorophyll — Properties  of  chlorophyll — 
Varying  tints — Synthesis  of  food — Acquisition  of  chloro- 
phyll— Autumnal  leaf-fall — Withdrawal  of  leaf-substance 
— Color  as  a  protecting  screen — Separation  layer — Ever- 
green leaves. 


CONTENTS 


X.   The  Significance  of  Color,  D.T.  MacDougal..165 

Early  views — Sprengel's  discoveries — Ecological  consider- 
ations— Enumeration  of  colors— Chlorophyll— Etiolin — 
The  lipochromes — Anthocyans— Relation  of  anthocyan 
to  light — The  screen  theory — Promotion  of  metabolism 
— Promotion  of  transpiration — Red  seaweeds — Mark- 
ings not  due  to  color — Silvery  areas — Velvety  surfaces 
— Conclusions. 

XL    The  Right  to  Live,  J.  C.  Arthur 193 

Aggressiveness  of  plants — Likeness  of  plants  and  animals 
— Possible  rate  of  increase — Weeds  as  examples — Prolifi- 
cacy of  other  plants — Illustrative  similes — A  world  of 
strife — Destruction  of  life  for  a  dinner — Natural  right  to 
food— Logic  of  good  fortune — Object  of  living— Death  not 
essential  to  life — Plants  are  born  to  live — Right  to  life 
should  be  respected. 

XII.  Distinction  between  Plants  and  Animals, 

J.  C.  Arthur 209 

Learned  vagaries — Ancient  opinions — Modern  opinions — 
An  intermediate  kingdom-Blending  of  the  two  kingdoms- 
Characters  from  structure  and  function — Various  physio- 
logical distinctions — The  most  universal  structures — 
Characters  to  be  taken  from  the  active  organism — Repro- 
ductive states  to  be  ignored — Animals  and  plants  defined 
— Chemical  features  of  cell  walls — Physical  features  of 
cell  walls — The  test  applied. 

XIII.  Index  to  Plant  Names 229 


THE  SPECIAL  SENSES  OF   PLANTS. 

Aside  from  the  tales  of  travelers,  the  varied 
plant  myths,  and  the  inventions  of  story 
writers,  there  have  been  fancies  and  beliefs 
held  by  learned  men  in  past  ages,  which  in- 
vested ])lants  with  specific  powers  differing 
from  those  of  animals  only  in  clearness  of 
manifestation.  Not  until  the  middle  of  the 
present  century,  however,  did  the  commonly 
observed  movements  of  plants  receive  any 
genuine  interpretation.  Aristotle  and  his  fol- 
lowers to  the  time  of  Cesalpino  (1583), 
vaguely  ascribed  a  soul  to  plants  which  di- 
rected their  vital  operations  and  distinguished 
them  from  lifeless  nature.  Jung,  a  contem- 
porary of  Kepler,  Galileo  and  Descartes,  who 
dominated  botanical  thought  in  Germany 
during  the  seventeenth  century,  expressed  his 

*Condensed  from  a  presidential  address  before  the  Indiana 
Academy  of  Sciences,  December  27,  1893. 


nsmnTY  unuxr 
JV.  C.  Stoe  C^Uttt 


LIVING  PLANTS 


Eighteenth 

century 

opinions 


view  in  the  sentence:  ''Plfinta  est  corpus  viv- 
ens  not!  sentiens.''  A  hundred  years  later 
Linnaeus  gave  his  famous  definition  of  the 
three  kingdoms  of  nature:  "Minerals  grow, 
plants  grow  and  live,  animals  grow,  live  and 
feel."  These  great  leaders  of  scientific  thought 
inclined  to  deny  sentience  to  plants  as  a  mat- 
ter of  definition,  but  did  not  wholly  discoun- 
tenance some  of  the  vagaries  of  their  predeces- 
sors. 

At  the  beginning  of  the  present  centurj- gen- 
eral students  of  plant  life  were  inclined  to 
admit  greater  range  of  the  plant's  powers. 
Sir  J.  E,  Smith,  in  his  "Introduction  to 
Botany,"  a  work  which  met  with  such  favor 
as  to  pass  through  seven  editions  within 
twenty-six  years,  has  voiced  the  uncertainty 
of  the  period  regarding  the  plant's  status  in 
the  form  of  a  query:  "As  they  possess  life,  ir- 
ritability and  motion,  spontaneously  direct- 
ing their  organs  to  what  is  natural  and  bene- 
ficial to  them,  and  flourishing  according  to 
their  success  in  gratifying  their  wants,  may 
not  the  exercise  of  their  vital  functions  be  at- 
tended with  some  degree  of  sensation,  how- 
ever low,  and  some  consequent  share  of  hap- 
piness?" Erasmus  Darwin,  a  few  years  be- 
fore, and  J.  E.  Tupper,  a  few  years  later,  ex- 
pressed similar  sentiments  in  works  that  met 
with  popular  recognition  and  approval. 


SPECIAL  SENSES 


The  passing  of  the  present  century  has  seen 
an  increasing  tendency  toward  the  serious 
use  of  terms  for  plant  activity  borrowed  from 
the  volitional  and  neural  manifestations  of 
animals.  These,  in  part,  are  suggested  by 
purely  superficial  analogy,  and  intended  sole- 
ly to  lend  greater  attractiveness  to  the  narra- 
tive, as  in  Charles  Darwin's  description  of  a 
twining  plant,  whose  horizontal  extremity 
repeatedly  slid  past  the  support  which  tem- 
porarily arrested  its  progress  as  it  swung 
slowly  around  in  a  circle.  "This  movement 
of  the  shoot  had  a  very  odd  appearance,"  he 
says,  "as  if  it  were  disgusted  with  its  failure, 
but  was  resolved  to  try  again."  Yet  in  part 
there  is  implied  an  obscure  but  real  analogy, 
as  when  the  same  author  in  another  ^vork 
sums  up  his  studies  of  the  root  tip  with  the 
assertion  that  in  its  power  to  direct  move- 
ment in  the  adjoining  parts  it  "acts  like  the 
brain  of  one  of  the  lower  animals." 

So  long  as  the  comparison  of  animal  and 
vegetable  activities  rested  largely  upon  exter- 
nal appearances,  with  very  limited  under- 
standing of  the  changes  within  the  organism 
by  which  they  are  brought  about,  no  consid- 
erable advance  was  possible.  At  first  the  in- 
terpretation was  necessarily  based  upon 
human  and  animal  analogies.  As  Julius  Sachs 
has    admirably    said    in    his    "History    of 


Application 
of  terms 


Knowledge 
of  mechanism 


LIVING  PLANTS 


Botany,"  "from  our  own  vital  motions  we 
argue  to  those  of  the  higher  animals,  which 
we  comprehend  immediateh^  and  instinctively 
from  their  conduct;  by  aid  of  these  the  mo- 
tions of  the  lower  animals  also  become  intel- 
ligible to  us,  and  further  conclusions  from 
analogy  lead  us  finally  to  plants,  whose  vi- 
tality is  only  in  this  way  made  known  to  us." 
An  illustration  of  such  reasoning  is  admira- 
bly set  forth  by  G.  H.  Lewes,  the  eminent 
English  psychologist,  in  his  volume  on  the 
object,  scope  and  method  in  the  study  of  psy- 
chology. He  says :  "Touch  the  eye  of  a  frog, 
and  there  is  at  once  the  response  of  a  reflex 
closure  of  the  eyelid.  Touch  the  hairs  of  a 
venus  fly-trap  {Dionoea muscwula) ,  and  there 
is  at  once  the  response  of  a  reflex  closure  of 
the  leaf.  Confine  the  frog  and  the  dionoea 
under  a  glass  shade,  and  place  there  a  sponge, 
over  which  ether  has  been  sprinkled.  Both 
plant  and  animal  breathe  this  air  in  which 
there  is  vapor  of  ether,  and  as  this  vapor  pen- 
etrates to  their  tissues  we  observe  a  gradual 
cessation  of  all  sensibility ;  first  the  reflex 
actions  cease,  then  the  irritability  of  the  par- 
ticular tissues  ceases.  Stupor  has  supervened 
for  both.  Now^  remove  the  glass  shade;  the 
vapor  dissipates,  the  fresh  air  penetrates  to 
the  tissues  in  exchange  for  the  vitiated  air, 
and  both  frog  and  dionoea  slowly   recover 


SPECIAL  SENSES 


their  sensibility."  From  this  experiment  he 
justly  concludes  "that  the  animal  and  plant 
organisms  have  with  their  common  structure 
common  properties,  and  if  we  call  one  of  these 
properties  sensibility  in  the  animal,  we  must 
call  it  thus  in  the  plant." 

Modern  investigations  have  more  and 
more  confirmed  the  fundamental  unity  of  Primary 
the  primary  functions  of  animals  and  plants,  "nity 
but  at  the  same  time  have  increasingly  em-  J^**^  ^f^^t 
phasized  the  great  divergence  they  have  ob-  ^'^^'^"^^ 
tained  in  developing  along  lines  of  specific 
adaption  to  the  needs  of  the  energy -liberating 
animal  on  the  one  hand,  and  of  the  energy- 
conserving  plant  on  the  other  hand.  Until 
recently  the  difficulty  of  interpreting  the 
movements  of  plants  without  recourse  to  the 
assumption  of  a  structural  device  in  someway 
comparable  to  the  neuro-muscular  mechanism 
of  animals  has  seemed  very  great.  But  the 
wonderful  advance  in  studying  the  plant's 
minute  structure  and  general  physiology  dur- 
ing the  last  few  decades  has  revealed  unsus- 
pected and  ample  vegetal  methods  of  bringing 
about  movement  as  the  result  of  stimulation, 
which  bear  no  analogy  and  no  counterpart  to 
those  of  animals,  but  have  been  developed 
with  a  trend  as  different  as  the  physical  basis 
of  tissues  in  the  plant  is  different  from  that  in 
the  animal. 


vIVING  PLANTS 


If  we  ask  ourselves  what  could  properly  be 
Wh  nstitute  considered  as  constituting  special  senses  in 
special  senses  plants,  it  will  be  necessary  to  remember  that 
in  the  broadest  ecological  import  the  special 
senses  of  animals  are  the  conspicuous  ways 
in  which  they  respond  to  particular  kinds  of 
external  stimuli  in  promoting  their  well-being, 
and  that  the  same  must  be  true  of  plants. 
Knowing  that  irritability  is  a  fundamental 
property  of  all  living  matter,  let  us  see  w^hat 
advantages  the  animal  and  the  plant  could 
secure  by  its  special  development. 

It  is  unquestionable  that  the  paramount 
necessity  of  every  organism  is  self-preserva- 
tion. To  secure  food,  to  avoid  injury,  and  to 
obtain  the  requisite  supply  of  light,  heat, 
moisture  and  air,  may  be  considered  the  funda- 
mental necessities  of  every  living  being, 
whether  man  or  monad,  tree  or  microbe.  It 
is  in  these  directions,  therefore,  that  we  must 
look  for  special  senses. 

The  animal  has  developed  a  quick  response 
Sense  of  to  contact.    This  is  probably  the  most  univer- 

contact  sal  of  all  the  senses,  and  in  its  lowest  forms 

is  little  removed  from  simple  irritability.  It 
primarily  contributes  to  the  animal's  safety, 
as  it  gives  warning  of  the  proximity  of  uncon- 
genial or  dangerous  objects,  and  is  also  an 
important  factor  in  the  operation  of  securing 
food,  and  in  many  minor  operations.    It  is  a 


SPECIAL  SENSES 


characteristic  sense  in  well  nigh  every  animal, 
and  in  the  larger  number  is  especially  devel- 
oped and  intensified  in  certain  organs  that 
may  be  appropriately  termed  organs  of  touch. 

If  we  return  to  plants,  we  find  this  simplest 
and  most  generalized  of  senses,  with  some 
notable  exceptions,  practically  absent.  In  a 
few  instances,  as  in  the  tendrils  of  certain 
plants,  there  is  a  marked,  sometimes  a  mar- 
velous sensitiveness  to  touch,  but  it  is  con- 
nected neither  with  the  attainment  of  safety 
nor  of  food.  Only  in  the  very  few  and  excep- 
tional cases  of  insectivorous  plants,  like  the 
sundews,  has  the  plant  acquired  a  sense  of 
touch  to  aid  it  in  detecting  and  grasping  food . 
But  sensitiveness  to  contact  is  not  a  common 
property  of  plants. 

An  inquiry  into  the  conspicuous  difference 

between  the  attitude  of  the  animal  and  the     -r     j   t 

1  rend  or  sense 
plant  toward  objects  external  to  itself  must  development 
reveal  some  of  the  reasons  underlying  the 
trend  of  sense  development.  And  first  of  all 
it  must  be  noted,  that  when  the  animal  de- 
tects something  inimical  to  its  safety,  it 
moves  away  from  the  offending  object,  a  pro- 
cedure impossible  to  the  plant  with  its  anchor- 
age of  roots.  Were  the  aspen  quaking  through 
fearof  impending  calamity,  it  could  not  escape 
by  flight,  or  by  the  displacement  of  its  body 
by  so  much  as  an  inch.    In  another,  and  even 


LIVING  PLANTS 


more  important  particular,  does  the  animal 
with  its  power  of  locomotion  show  the  need 
of  a  different  set  of  senses  from  those  of  the 
plant.  The  ingestion  of  a  large  amount  of 
solid  food  requires  the  animal  to  search  for  a 
suitable  supply;  while  the  plant,  partaking 
only  of  food  in  solution  and  in  comparatively 
small  quantities,  is  enabled  to  secure  it  by 
slender  feeders  extending  into  the  surround- 
ing medium.  In  securing  food  and  protecting 
itself  from  injury  the  animal  makes  use  of 
three  important  senses:  smell,  hearing  and 
sight.  The  plant  with  its  fixed  position  and 
simpler  requirements  does  not  need  these 
senses  ;  they  would  be  useless  to  it,  and  have 
not  been  developed. 

We  may  safely  conclude  that  in  so  far  as 

animals    and    plants    respond    in   a  marked 

Free  and  fixed     "^^nner  to  stimulatic»n,  it  is  along  two  dis- 

organisms  tinct  lines,  to  correspond  with  the  necessities 

of  free  organisms  on   the  one  hand,  and  of 

fixed  organisms  on  the  other. 

For  a  fixed  organism  orientation  is  of  prime 
necessity.  The  roots  of  a  plant  must  pene- 
trate the  soil  and  its  foliage  be  spread  to  the 
air. 

Yet  the  root  or  shoot  has  no  power  to  de- 
viate from  extension  in  a  straight  line  unless 
it  is  acted  on  by  some  external  force,  no  more 
than  a  cannon  ball  or  other  moving  body  has 


SPECIAL  SENSES 


power  to  vary  from  a  straight  line.  If  a  seed 
in  germinating  lies  in  such  a  position  that  the 
roots  point  upwards  and  the  stem  down- 
wards, some  method  is  needed  by  which  the 
plantlet  may  readjust  itself,  either  by  turning 
over  bodily,  or  changing  the  direction  of  its 


Fig  1  —A  cHnostat.  Germinating  seeds  are  pinned  on  the 
cork  disc,  and  are  kept  moist  by  dipping  into  water  as  they 
revolve.  One  revolution  is  made  in  about  twenty  mmutes. 
Under  these  conditions  the  primary  root  and  stem  grow 
straight  in  whatever  position  they  are  fastened. 

growing  parts.  As  every  one  knows,  the  lat- 
ter alternative  is  adopted,  and  the  roots  bend 
down  and  penetrate  the  earth,  while  the  stem 
bends  up  and  hfts  its  foliage  into  the  air.  It 
is  so  apparently  a  matter  of  course  that 
stems  grow  up  and  roots  grow  down,  that 
we  may  never  have  given  a  thought  to  an 
explanation  of  the  process.  Even  botanists 
have  only  recently  felt  the  full  necessity  for 
an  explanation  of  the  fact,  as  it  has  been  less 
than  two  decades  since  Vochting  announced 
his  theory    of  rectipetahty,   or  the  inherent 


LIVING  PLANTS 


gravity  sense 


tendency  of  growing  organs  to  extend  in  a 
straight  line  unless  acted  upon  by  outside  force. 
There  is  only  one  force  known  that  acts  uni- 
rrA^^^fir^L  formly  in  the  direction  of  the  center  of  the 
earth,  that  is  gravity  ;  and  it  was  the  genius 
of  Andrew  Knight,  an  Englishman,  to  demon- 
strate as  long  ago  as  1806,  that  this  force 
does  furnish  the  directive  influence  in  securing 
verticality  to  plants.  He  grew  plants  on  re- 
volving wheels,  and  found  that  they  respond- 
ed to  centrifugal  force,  and  that  when  the 
wheel  was  placed  horizontally  and  revolved 
at  a  speed  that  made  the  centrifugal  force 
equal  to  that  of  gravity,  both  roots  and 
stems  grew  obliquely,  taking  the  position  of 
a  resultant  of  the  two  forces,  that  is,  of  forty- 
five  degrees  to  the  vertical. 

But  this  discovery  by  Knight  was  not  imme- 
diately fruitful,  for  no  one  could  tell  how  grav- 
ity produced  the  effect  ascribed  to  it.  If  it 
pulled  the  root  down,  why  did  it  push  the 
stem  up?  The  stem  is  as  heavy  as  the  root, 
why  are  not  both  attracted  toward  the  center 
of  the  earth?  It  was  a  curious  paradox  to 
say  the  same  force  acted  now  one  way  and 
now  exactly  the  reverse  on  different  parts  of 
the  same  plant ;  as  if  pulling  and  pushing 
were  the  same  thing.  It  was  supposed  that 
gravity  acted  upon  the  root  as  it  does  upon  a 
mass  of  taffy  candy,  drawing  it  downward. 


SPECIAL  SENSES 


But  Sachs  showed  in  1873  that  the  root  of  a 
bean  fixed  horizontally  over  mercury  could 
penetrate  the  mercury  in  assuming  a  vertical 
position.  As  mercury  is  about  thirteen  times 
as  heavy  as  the  tissues  of  a  young  root,  it  is 
evident  that  far  more  force  was  expended  in 
penetrating  the  mercury  than  could  have  been 
derived  from  the  physical  action  of  gravity, 
that  is,  from  the  simple  weight  of  the  root. 
The  experiment  has  since  been  tried  in  another 
and  more  obvious  way  by  harnessing  a  root 
tip  lying  horizontal  to  a  weight  suspended 
over  a  pulley,  the  weight  being  raised  as  the 
root  bends  downward  in  response  to  gravity. 
From  these  experiments  we  must  conclude 
that  gravity  does  not  act  physically  but  phys- 
iologically to  induce  the  curvature,  that  is,  it 
acts  as  a  stimulus.  It  is  a  small  spark  that 
fires  the  gun.  The  spark  will  fire  a  pistol  or 
a  cannon,  the  result  depending  solely  upon  the 
amount  and  arrangement  of  the  explosive 
material.  So  in  theroot,if  thereis  the  proper 
mechanism  and  storage  of  force,  gravity  will 
release  this  force  and  cause  the  bending,  the 
amount  of  work  done  being  enormously  out 
of  proportion  to  the  initial  expenditure  of 
energy. 

But  when  the  bending  takes  place,  will  it  be 
upward  or  downward  ?  If  it  were  a  purely 
mechanical  device,  it  is  evident  that  by  know- 


LIVING  PI.ANTvS 


ing  the  structure  of  the  organ,  one  could  pre- 
dict the  direction  of  movement  under  stimu- 
lation. But  we  shall  have  to  look  beyond 
and  above  simply  mechanical  laws  for  an  ex- 
planation, for  the  living  organism  acquires 
specific  powers  of  adaptation  and  heredity. 

Although  the  force  which  a  plant  can  exert 
amounts  to  several  atmospheres,  it  is  only  in 
the  young  tender  portions,  usually  at  the  ends 
of  the  branches  of  the  stem  and  root,   that 
Movement  ^^^^  force  can  be  successfully  applied  to  secure 

connected  movement  of  the  whole  organ.      It  therefore 

with  growth  comes  about  that  movement  in  plants  is 
oftenest  associated  with  growth.  This  ar- 
rangement permits  each  root  tip  and  growing 
stem  to  have  its  own  kind  and  degree  of  sen- 
sitiveness. Thus  we  find  by  experiment  that 
while  the  first  root  which  starts  from  a  seed, 
the  tap  root,  is  sensitive  to  gravity  in  such  a 
way  that  it  places  itself  parallel  to  the  direc- 
tion of  the  impinging  force  and  points  directly 
downward,  the  secondary  roots,  which 
branch  from  it,  are  sensitive  after  a  different 
fashion,  and  instead  of  growing  parallel  to 
the  force,  grow  at  an  angle  to  it,  the  exact 
angle  being  different  for  different  kinds  of 
plants.  The  tertiary  roots,  or  next  set  of 
branches,  are  usually  very  little  sensitive  to 
gravity,  or  if  they  are  sensitive  they  assume  a 
nearly  horizontal  position.      The  stems  react 


SPECIAL  SENSES 


Transmission 


in  a  similar  way,  except  that  the  general 
direction  is  upward  instead  of  downward, 
and  in  consequence  of  the  diversity  of  sensi- 
tiveness of  the  primary  and  secondar}^  shoots, 
the  branches  are  spread  out  to  the  air  and 
light,  imparting  to  each  species  of  tree  and 
herb  its  characteristic  appearance. 

But  if  there  is  no  nerve-like  communication 
between  one  root  tip  and  another,  or  between 
one  stem  and  another,  there  is  sometimes  a 
distinct  transmission  of  impulse  from  the  cells 
receiving  the  stimulation  to  the  cells  a  short  ^f  impulse 
distance  away  where  the  movement  is  con- 
summated. Thus,  in  the  tip  of  the  primary 
root  Darwin  found  that  only  the  cells  at  the 
very  tip  were  sensitive.  If  so  small  a  piece  as 
one  millimeter  be  removed  from  the  end  of  the 
root  by  cutting  or  burning,  all  power  of 
movement  is  lost.  This  remarkable  localiza- 
tion has  been  denied  by  Sachs  and  Detlefsen, 
who  characterize  Darwin's  claim  as  sensation- 
al, but  the  fact  has  been  fully  verified  by  Wies- 
ner,  who  found  that  if  the  root  is  weakly 
sensitive,  the  seat  of  irritability  coincides 
with  the  zone  of  most  rapid  growth,  but  if 
highly  sensitive, it  will  beat  a  distance. 

To  sum  up  the  characteristics  of  the  gravity 
sense :  It  is  localized  in  or  near  the  ends  of 
growing  roots,  stems  and  other  organs  of  the 
plant ;  it  is  developed  in  varying  strength  in 


LIVING  PLANTS 


different  organs ;  it  sets  up  movement  of  the 
organ  in  response  to  stimulation  ;  the  direction 
of  movement  will  depend  upon  the  specific 
kind  of  sensibility  acquired  by  that  organ ; 
the  direction  of  the  movement  will  always 
bear  some  definite  relation  to  the  vertical 
without  regard  to  the  position  of  the  plant. 
But,  what  other  senses  have  plants  ?  Next 
to  a  proper  position,  most  plants  need  a  suit- 
able exposure  to  light.  I  shall  not  attempt 
Sensitiveness  />/3^^  t^  *°    show    the   nu- 

to  light  (^-fc«_f^^^^\  merous  and  inter- 

esting ways  in 
which  plants  re- 
spond to  light. 
Everyone  knows 
how  plants  light- 
ed from  one  side, 
as  when  placed 
before  a  window, 
bend  toward  the 
light.  This  is  a 
true  sensitiveness, 
for  it  results  in 
bringing    about 


Fig.  2. — Charlock  seedlings  grow- 
ing in  a  glass  of  water  before  a  win- 
dow. The  stems  bend  toward  the 
light  and  the  roots  away  from  it. 


definite  movement. 
The  stems  place  themselves  parallel  to  the  di- 
rection of  the  incident  rays — that  is,  point  to- 
ward the  window,  while  the  leaves  place  them- 
selves at  right  angles  to  the  direction  of  the 


SPECIAL  SENSES 


light— that  is,  with  their  upper  surfaces  to  the 
window.    Leaves  and  stems,  therefore,  show 


^^  1  2/bf>   pojitior). 


Fig.  3. — Day  and  night  positions   of  the  leaves  of  redbud 
Cercis  Canadensis). 


Chemical  sense 


16  LIVING  PLANTS 

sensitiveness  characteristic  of  each.  Some 
stems,  however,  Hke  those  of  the  Virginia  creep- 
er, turn  away  from  Hght,  enabhng  them  to 
cUng  to  dark  walls.  Roots  which  are  general- 
ly buried  in  the  soil,  rarely  exhibit  sensitive- 
ness to  light,  and  when  they  do,  it  is  usually 
to  turn  from  it.  If  light  comes  to  the  organ 
from  two  directions,  it  will  bend  toward  the 
source  of  the  stronger  light,  and  differences 
which  will  affect  the  plant  are  far  more  minute 
than  can  be  detected  by  the  eye. 

As  in  the  case  of  roots,  certain  stems  place 
themselves  not  parallel  with  the  direction  of 
the  light,  but  at  some  particular  angle  to  it, 
in  accordance  with  some  inherent  necessity. 
Not  as  large  a  part  of  the  plant,  as  a  rule,  is 
as  sensitive  to  light  as  to  gravity,  but  the  de- 
gree of  sensitiveness  is  often  greater. 

Plants  also  possess  a  chemical  sense,  a  kind 
of  taste,  by  which  they  detect  certain  sub- 
stances in  solution  fitted  for  their  nutrition. 
By  this  means  parasitic  fungi  starting  to 
grow  upon  the  surface  of  other  plants  find 
their  way  into  the  stomata  from  which  the 
acid  juices  of  the  tissues  diffuse,  and  thus  gain 
entrance  into  the  host.  Roots  exhibit  sensi- 
tiveness to  many  nutritive  substances,  al- 
though not  as  a  rule  to  the  same  extent  that 
fungi  do.  It  enables  them  to  turn  and  grow 
in  the  direction  of  the  best  food  supply,  and 


SPECIAL  SENSES 


accounts  for  the  popular  notion  that  roots 
seek  rich  soil. 

Moisture  also  exerts  a  directive  influence 
upon  roots,  and  sometimes  upon  other  parts 
of  the  higher  plants,  as  well  as  upon  the  or-  „  , 
gans  of  many  lower  plants.  Usually  the 
movement  is  toward  the  moister  side.  It  is 
evidently  beneficial  to  the  plant  in  keeping  its 
absorbing  organs  bathed  in  the  greatest 
available  supply   of  fluid. 

Plants  are  thus  seen  to  react  sensitively  to 
gravity,  light,  solutions,  moisture  and  con- 
tact. Each  is  a  special  kind  of  sensitiveness, 
having  its  own  method  of  reaction.  Two  or 
more  kinds  of  sensitiveness  may  reside  in  the 
same  organ,  when  its  position  will  be  a  re- 
sultant of  the  several  forces.  There  are  no 
exclusive  organs  of  sense  in  plants,  although 
there  is  more  or  less  localization  in  certain 
parts ;  and  there  are  no  nerves  although  the 
motor  impulse  may  be  transmitted  some  dis- 
tance, even  as  far  as  seventy  centimeters  or 
more  in  very  vigorous  sensitive  plants,  for 
example  in  mimosa.  To  complete  the  com- 
parison I  should  say  there  are  no  muscles  in 
plants,  although  they  execute  movements  of 
very  considerable  amplitude.  Their  motor 
mechanism  is  operated  by  devices  having  no 
counterpart  in  the  animal  organization,  but 
is  the  outcome  of  specific  adaptation. 


LIVING  PLANTS 


Aristotle's  notion,  which  is  still  too  preval- 
ent, of  an  ascending  complexity  in  vital  phe- 
nomena from  plants  to  man,  should  be  whol- 
ly abandoned.  The  only  way  of  viewing  or- 
ganic nature,  to  secure  proper  interpretation, 
is  that  of  two  diverging  lines  of  development, 
one  through  motile  forms,  and  the  other 
through  fixed  forms.  Each  line  of  develop- 
ment has  worked  out  peculiarities  of  its  own. 
If  the  special  senses  of  animals  show  wonder- 
ful adaptations,  the  special  senses  of  plants, 
although  very  dissimilar,  will,  when  better 
known,  appear  quite  as  remarkable. 

The  observation  of  Sachs,  the  learned  pro- 
fessor of  Wiirzburg,  and  one  of  the  most  far- 
seeing  of  ph^^siological  botanists,  is  particu- 
larly pertinent  in  this  connection.  "We  have 
no  necessity,"  he  says,  "to  refer  to  the  physi- 
ology of  nerves  in  order  to  obtain  greater 
clearness  as  to  the  phenomena  of  irritability 
in  plants;  it  will,  perhaps,  on  the  contrary, 
eventually  result  that  we  shall  obtain  from 
the  process  of  irritability  in  plants  data  for 
the  explanation  of  the  physiology  of  nerves, 
and  this,  although  it  is  as  yet  a  distant  hope, 
gives  a  special  attraction  to  the  study  of  the 
irritable  phenomena  of  plants." 


THE   DEVELOPMENT   OF   IRRITABILITY 


The  economical  acquisition  of  nutritive  sub- 
stance in  proper  amount  is  a  fundamental  ne- 
cessitj'  of  every  organism,  and  to  the  condi- 
tions attendant  upon  the  performance  of  the 
nutritive  functions  must  be  ascribed  the  chief 
causes  underlying  the  development  of  the  plant 
body.  The  chlorophyll  processes  have,  there- 
fore, been  the  paramount  factors  in  the  devel- 
opment of  the  shoot,  and  the  absorptive  pro- 
cesses have  ruled  the  differentiation  of  the  root 
system. 

In  an  early  stage  of  the  existence  of  the  an- 
cestors of  our  present  plant  population  they      j-j   .     .. 
were  doubtless  thalloid  organisms,  unicellular     existing  forms 
or  multicellular,  floating  in  the  water,  and 
were  perhaps  in  many  instances  endowed  with 

•Given  in  an  address  before  the  Botanical  Club  of  the  Univer- 
sity of  Chicago,  Jan.  18,  1897. 


20  LIVING  PLANTS 

the  power  of  locomotion.  All  of  the  cells  con- 
tained chlorophyll  and  shared  in  the  work  of 
food  formation,  and  since  more  or  less  of  the 
surface  of  each  cell  was  bathed  by  the  fluid  in 
which  it  lived,  all  absorbed  the  mineral  salts 
in  solution  in  the  surrounding  medium,  and 
all  of  the  cells  participated  in  the  reproductive 
processes. 

It  will  not  be  profitable  here  to  follow  the 
direction  or  possibilities  of  morphological  dif- 
ferentiation into  detail,  except  to  say  that  the 
organism  soon  found  it  more  economical  to 
be  attached  to  a  fixed  point  rather  than  to 
float  at  random  or  swim  through  the  water 
which  contained  the  mineral  salts  in  equal 
diffusion,  and  in  which  the  necessary  intensity 
of  light  bore  a  direct  relation  to  the  distance 
from  the  surface.  Then  in  consequence  of  this 
newly  acquired  habit  of  fixation,  and  the  re- 
cession of  the  water  from  the  substratum  occu- 
pied, some  distinct  and  important  physiolog- 
ical changes  ensued  to  meet  the  new  condi- 
tions attendant  upon  the  nutritive  processes. 
The  sunlight  impinging  upon  the  portion  of 
Chlorophyll  the  plant  containing  chlorophyll  no  longer 
and  sunlight  came  filtering  down  through  layers  of  water 
of  varying  depth,  but  beat  upon  it  from  all 
points  in  an  arc  of  one  hundred  and  eighty  de- 
grees. The  greater  amount  of  energy  thus 
available  to  the  aerial  shoot  could   only  be 


IRRITABILITY 


made  of  use  to  the  plant  by  the  arrangement 
and  division  of  its  chlorophyll  areas,  and 
the  morphological  necessities  will  account 
for  the  method  of  differentiation  of  the 
shoot,  and  the  very  great  degree  of  segmen- 
tation and  branching  which  it  has  attain- 
ed. The  segmentation  of  the  shoot  has  made 
possible  not  only  the  profitable  display  of 
ever -increasing  areas  of  chlorophyll-bearing 
tissues,  the  proper  elevation,  orientation  and 
isolation  of  the  reproductive  organs,  but  also 
a  separation  of  the  minor  functions  and  the 
differentiation  of  special  organs  for  their  per- 
formance. The  separation  of  nutritive,  repro- 
ductive and  other  functions  has  been  accom- 
panied by  a  contemporaneous  separation  and 
development  of  the  special  forms  of  irritabil- 
ity which  are  concerned  with  the  forces  dealt 
with  by  each  organ.  Thus,  for  example,  the 
most  important  factor  in  the  processes  carried 
on  by  the  leaf  is  the  radiant  energy  derived 
from  the  sun.  As  a  necessary  concomitant  of 
the  advantageous  use  of  this  energy,  the  leaf 
has  developed  a  strongly  marked  irritability 
to  light  and  heat  rays. 

By  these  special  powers  it  is  enabled  to 
move  its  chlorophyll-bearing  areas  in  the 
leaves  into  such  position  that  theexact  inten- 
sity of  light  and  heat  rays  suitable  to  its 
specific  constitution  will  be  received  and  as  a 


LIVING  PLANTS 


Pollination 


Organization 
of  shoot 


result  of  the  relations  of  the  organ  to  the  ho- 
rizon in  response  to  its  heliotropism  and  ther- 
motropism, it  has  also  acquired  in  some  in- 
stances a  trace  of  geotropism.  The  elimina- 
tion of  all  but  nutritive  functions  from  the 
leaves  has  made  it  possible  for  these  organs 
to  perform  such  functions  with  greater  eco- 
nomy, and  made  superfluous  also  the  pres- 
ence of  any  other  forms  of  irritability  which 
would  direct  the  position  of  the  leaf. 

In  the  accomplishment  of  the  reproductive 
process,  an  incidental  condition  is  the  trans- 
ferance  of  the  pollen  from  its  place  of  forma- 
tion to  the  surface  of  the  stigma  in  the  same 
or  other  flowers.  In  a  great  majority  of  in- 
stances the  relation  of  the  line  adjoining  the 
anther  and  the  stigma  to  the  vertical  or  hori- 
zon, is  of  the  utmost  importance,  whether 
the  pollination  is  accomplished  automatically, 
by  air  currents,  or  by  insects,  and  a  well 
marked  geotropic  reaction  is  therefore  gen- 
erally exhibited  by  flowers  with  the  motor 
zone  located  in  the  peduncle.  These  organs 
also  show  minor  heliotropic  reactions. 

The  same  process  of  analysis  may  be 
applied  to  the  entire  shoot,  with  the  general 
result  that  each  organ  will  be  found  to  re- 
spond to  a  number  of  forces  generally  limited 
to  two  or  three,  though  of  course,  instances 
are  not  lacking  where  a  greater  number    of 


IRRITABILITY 


forms  of  irritability  are  found  to  reside  in  the 
same  organ,  as  for  example,  in  tendrils.  In 
such  instances,  however,  the  excessive  num- 
ber of  the  forms  of  irritability  have  beeen  de- 
veloped to  meet  special  ecological  conditions, 
bearing  upon  both  the  nutritive  and  repro- 
ductive processes  either  directly  or  indirectly. 
Furthermore,  the  organs  of  the  shoot  may 
also  acquire  the  pov^er  of  special  reactions  to 
internal  forces  or  stimuli,  such  for  example, 
as  the  carpotropic  movements. 

In  a  consideration  of  the  localization  and 
distribution  of  the  property  of  irritability, 
attention  is  to  be  called  to  the  fact,  that  the 
conditions  concerned  in  the  nutritive  processes 
of  the  shoot  show  an  invariably  wide  diffu- 
sion. Carbon  dioxide  exists  everywhere  in 
the  atmosphere  in  uniform  proportions  and 
bathes  every  part  of  the  shoot.  Sunlight  is 
bounded  only  by  the  horizon  line  and  may 
reach  any  surface  of  the  shoot  in  diffuse  form. 
The  chlorophyll  processes  may  then  be  carried 
on  by  the  sub-epidermal  tissues  in  any  por- 
tion of  the  shoot,  and  as  a  consequence,  a 
greater  proportion  of  the  peripheral  proto- 
plasm of  the  shoot  has  developed  an  irrita- 
bility to  sunlight,  although  it  may  not  al- 
ways be  manifested  by  organic  or  external 
movement,  or  other  response. 

The  researches  of  Rothert  have  shown  that 


Distribution 
of  nutritive 
factors 


LIVING  PLANTS 


a  large  part  of  the  surface  of  the  leaf  of  Ave- 
na  and  Phalaris  exhibits  a  heliotropic  sensi- 
bility, and  that  the  laminae  of  dicotyledonous 
leaves  exhibit  an  equal  distribution  of  sensi- 
tiveness over  their  entire  surface,  and  that  the 
leaflets  in  a  compound  organ  are  strictly  co- 
ordinate and  equal  with  respect  to  their  irri- 
tability. Those  branches  of  the  shoot  that 
have  developed  special,  or  ecological  adapta- 
tions exhibit  an  extension  of  the  irritable 
surface  corresponding  to  the  limited  diffusion 
or  occurrence  of  possible  stimuli,  modified  to 
some  extent  by  the  character  and  inclusive- 

e  ,         ness  of  the  reaction. 

Sensory  and  r  r       ^  •  i      •        t       i  • 

motor  zones  Before  further  progress  is  made  m  the  dis- 

cussion, the  chief  facts  in  the  organization  of 
the  irritability  of  leaves  should  be  recalled. 
The  portion  of  a  leaf  which  is  capable  of  re- 
ceiving light  and  converting  it  into  some 
other  force  which  will  set  up  a  reaction  is 
termed  the  sensory  zone.  The  portion  of  the 
organ  in  which  motion  ensues  is  termed  the 
motor  zone.  Now  as  may  be  seen  by  the  pre- 
ceding paragraph  the  sensory  zone  is  located 
in  the  blade  of  the  leaf,  and  if  the  movements 
of  the  leaves  of  the  bean  or  mimosa  are  ob- 
served, the  motor  zones  will  be  found  at  the 
base  of  the  petioles.  Light  striking  the  blade 
of  the  leaf  sets  in  action  a  second  force,  which 
is  transmitted  to  the  motor  zone  where  a  third 


N.  C.  State  C»««f« 


IRRITABILITY  25 

force  causes  the  movement.  The  leaf  then  is 
a  living  machine  the  movements  of  which  are 
directed  by  two  forces— light  and  heat  (some- 
times gravity),  while  the  root  is  directed  by 
many  forces. 

Although  the  motor  zones  of  the  shoots  do 
not  include  as  large  proportions  of  the  plant 
as  the  sensory  zones,  yet  the  distribution  is 
fairly  general  throughout  growing  regions. 
It  is  possible  to  induce  curvatures  in  some 
stems  in  which  growth  has  almost  entirely 
ceased.  The  curvature  is  accompanied  by  a 
revival  of  the  growth  activity,  however. 

Having  followed  the  shoot  to  its  ultimate  Development 
and  present  form  we  may  retrace  our  steps  to  r 
the  beginnings  of  the  root-system.  The  primi- 
tive function  of  the  root  of  the  plant  emerging 
from  an  aquatic  habit  was  of  course  purely 
mechanical  and  consisted  in  holding  the  or- 
ganism in  place.  With  the  recession  of  the 
water  the  plaut  no  longer  found  solutions 
of  mineral  salts  bathing  its  surface.  Its  rudi- 
mentary anchoring  organs  were,  it  is  true, 
left  in  contact  with  small  quantities  of  fluid, 
but  the  amount  of  surface  was  by  no  means 
adequate  or  proportional  to  the  now  rapidly 
enlarging  shoot.  Under  such  circumstances 
it  might  do  but  one  thing— extend  the  root- 
system  and  thereby  increase  its  absorbing 
surface. 


LIVING  PLANTS 


The  functions  of  the  root  are  not  so  numer- 
ous as  those  of  the  shoot,  and  while  the  effi- 
cient performance  of  the  necessary  amount 
of  absorption,  to  keep  pace  with  the  increase 
in  mass  and  surface  of  the  shoot,  has  de- 
manded a  repeated  branching,  yet  no  seg- 
mentation hke  that  of  the  shoot  has  occurred. 
The  less  important  function  of  the  root,  fixa- 
tion, is  purely  mechanical,  and  the  separation 
of  the  two  functions  has  not  been  effected  by 
a  localization  of  the  functions  in  different 
organs,  but  is  an  incident  to  the  stage  or 
degree  of  development  of  these  organs.  Phys- 
iologically the  basal  portion  of  roots  sustains 
a  relation  to  the  absorptive  system  similar  to 
that  of  the  basal  portions  of  typical  stems  to 
the  chlorophyll-bearing  and  reproductive 
organs. 

In  the  earlier  stages  of  growth  any  given 
portion  of  the  root  is  purely  directive,  next 
absorptive  and  in  the  later  periods,  is  exclu- 
sively fixative.  Only  in  certain  special  classes 
of  aerial  and  other  plants  does  a  separation 
or  isolation  occur.  The  stem,  on  the  other 
hand,  is  at  first  directive,  and  then  fixative, 
and  does  not  in  any  stage  of  its  existence  as- 
sume the  relative  importance  which  is  to  be 
ascribed  to  every  portion  of  the  root  in  one 
period  of  its  development. 

In  explanation  of  this  method  of  develop- 


IRRITABITITY 


ment,  so  widely  different  from  that  of  the 
shoot,  it  is  to  be  said  that  roots  have  taken 
on  fewer  functions,  and  have  always  been  sur- 
rounded by  much  more  uniform  conditions 
than  the  shoot,  and  in  consequence  have  met 
the  necessity  of  a  much  narrower  range  of 
adaptive  modifications.  But,  while  the  rapid- 
ity of  variation  of  outward  conditions  affect- 
ing roots  has  been  much  less  than  that  of  the 
shoot,  yet  the  greater  number  of  the  factors 
concerned  and  the  inequalities  of  diffusion  and 
distribution  of  the  nutritive  substances  are 
much  greater  than  those  affecting  the  shoot.  Nutritive 
Water  and  food  substances  lie  below  the  sur-  ^^^^^""^  ^  '°^^ 
face  of  the  substratum  and  the  root  has  de- 
veloped a  highly  marked  form  of  geotropism, 
which  enables  it  to  penetrate  the  soil.  Water 
and  food  substances  are  by  no  means  so  uni- 
formly distributed  as  sunlight  and  carbon  di- 
oxide, h  o  wever .  While  water  exhibits  a  fairly 
horizontal  distribution  in  quantity,  yet  so  far 
as  its  actual  availability  is  concerned,  differ- 
ences corresponding  to  the  physical  character- 
istics of  the  soil  are  to  be  found.  The  vertical 
distribution  is  modified  in  the  same  manner. 
The  mineral  food  substances  present  no  sys- 
tem or  uniformity  of  distribution  whatever. 
As  a  matter  of  fact  the  masses  of  food  sub- 
stances may  and  do  lie  in  all  possible  direc- 
tions from  the  absorbent  zone  of  the  apical 


LIVING  PLAN-TS 


portion  of  the  root.  In  order  to  reach  such 
irregularly  distributed  masses  of  nutritive 
substances,  it  is  evidently  necessary  that  the 
root  should  develop  an  irritability  to  a  much 
greater  number  of  forces  than  any  member  of 
the  shoot,  and  furthermore  it  is  evident  that 
all  the  forms  of  irritability  thus  acquired  must 
be  located  in  the  apical  portion  of  the  root, 
the  proper  directive  activity  of  which  only 
can  result  in  facilitating  the  absorptive  pro- 
cesses. The  coincidence  of  several  forms  of 
irritability  v^ithin  such  narrow  limits  has  ne- 
cessitated differentiations  in  another  direction 
from  that  offered  by  the  shoot.  The  differen- 
tiation of  the  shoot  resulted  in  a  tendency  to 
separate  the  different-  forms  of  irritability 
with  their  attendant  mechanisms.  The  in- 
crease of  the  efficiency  of  the  root  has  resulted 
in  the  acquisition  of  a  constantly  increasing 
number  of  forms  of  which  the  mechanism 
must  necessarily  be  identical.  Still  further, 
this  has  resulted,  of  course,  in  the  differentia- 
tion of  the  separate  parts  of  the  mechanism, 
and  increase  of  its  delicacy  of  reaction.  This 
may  be  held  to  apply  to  all  similar  arrange- 
ments, especially  in  the  ecological  adaptations 
exhibited  by  certain  members  of  the  shoot. 

Thus  if  an  examination  of  the  mechanism 
of  irritability  of  the  root  is  made,  it  will  be 
found  that  only  an  extremely  small  portion 


IRRITABITITY 


of  the  organ  raayreceive  a  stimulus  from  grav- 
ity, light,  temperature,  moisture,  running 
water,  chemicals,  electricity,  contact  or  injury. 
This  sensory  zone  consists  of  a  mass  of  cells  in 
the  shape  of  a  cylinder  beginningimmediately 
back  of  the  growing  point  and  not  more  than 
one  millimeter  in  length.  The  portion  of  the 
root  in  which  curvature  ensues  lies  immedi- 
ately back  of  the  sensory  zone. 

The  root  is  a  generalized  type  of  the  mech- 
anisms by  which  plants  respond  to  external 
directive  stimuli,  and  the  shoot  is  a  special- 
ized type.  The  same  mechanism  in  the  root 
is  capable  of  response  to  eight  different  classes 
of  stimuli,  while  in  the  shoot  but  two  or  three 
may  act  upon  any  given  organ,  in  such  man- 
ner as  to  secure  a  responsive  movement. 


yr-"'.^fc5^g««^^>^.-^^--^^^- 


III. 


WILD   LETTUCE   AS   WEED   AND   COMPASS   PLANT 


The  prickly  lettuce  is  a  plant  closely  resem- 
bling the  common  garden  lettuce,  especially 
the  narrow  leaved   Cos  varieties.     The  simi- 

laritv  is  more  striking  if  we  compare  them    ,  „ 

r      '    ■,      n  111  1  Likeness  to 

after  the  flower  stalks  have  begun  to  appear,    cultivated 

There  are  in  fact  good  grounds  for  believing    lettuce 

that  the  garden  forms  were  derived  from  the 

wild  lettuce :     a  view  held  at  one  time  by  Bis- 

chofif,  DeCandolle,  and  other  authorities,  who 

wrote  the  Latin  name  of  the  garden  forms 

Lactuca  Scariola  var.  sativa,  instead  of  L. 

sativa,  as  adopted  by  Linnaeus  and  adhered 

to  by  most  of  recent  writers. 

The  plant  is  an  annual,  coming  from   seed 

each  year.    Occasionally  the  seed  germinates 

in  the  fall,  the  plant  making  some  growth  be- 

*A  portion  of  Bulletin  No.  52  of  the  Indiana  Experiment  Sta- 
tion, issued  November  10,  1894. 


LIVING  PLANTS 


fore  the  cold  weather.  In  this  form  it  passes 
the  winter,  thus  becoming  a  winter  annual. 
The  term  is  applied  to  distinguish  such  plants 
from  true  biennials.  It  is  in  flower  from  July 
to  September. 

The  height  of  the  plant  is  from  a  few  inches 
in  poor  soil  up  to  five  or  six  feet,  or  more,  in 
rich  soil.  As  seen  along  fence  rows  and  in 
meadows  it  stands  as  a  rule  about  three  or 
four  feet  high.  In  general  the  plant  possesses 
a  central  straight  shaft,  branched  only  above. 
The  lower  half  or  two-thirds  of  the  stalk  is 
clothed  with  leaves  of  quite  uniform  width, 
four  to  six  inches  long  by  one  to  two  inches 
wide,  while  the  upper  half  or  third  of  the  stalk 
sends  out  spreading,  rather  bare  branches, 
much  subdivided,  and  ultimately  bearing  in- 
conspicuous yellow  flowers.  Each  flower 
(capitulum)  gives  rise  to  about  a  dozen  dark 
brown  (so-called)  seeds  of  similar  shape  to 
those  of  the  garden  lettuce,  but  somewhat 
shorter.  Each  seed  (in  reality  a  fruit,  con- 
sisting of  a  dry  capsule  inclosing  the  solitary 
small  seed,  like  all  members  of  the  composite 
family)  bears  a  slender  rigid  stalk  as  long  as 
itself,  in  turn  supporting  a  white,  filmy  para- 
chute, like  that  of  the  dandelion  seed,  only 
smaller,  which  serves  to  buoy  up  the  ripe  seed 
and  waft  it  long  distances  on  currents  of  air. 

The  whole  plant  has  a  pale,  pea-green  color. 


WILD  LETTUCE 


Its  Specially  characteristic  feature  is  the  pres- 
ence of  a  row  of  soft  prickles  along  the  edges 
of  the  leaf  and  a  row  down  the  midrib  beneath. 
There  are  also  a  few  prickles  scattered  over 
the  stem,  particularly  the  lower  portion. 
With  these  exceptions  the  plant  is  smooth. 
These  prickles  are  from  an  eighth  to  a  quarter 
inch  long,  and  although  scarcely  stiff  enough 
to  penetrate  the  flesh,  yet  give  the  plant  a 
rough  and  disagreeable  character  when  hand- 
led.    The  juice  of  the  plant  is  milky. 

The  prickly  lettuce  is  a  native  of  southern 
Europe,  northern  Africa,  and  the  temperate 
part  of  middle  Asia.  At  the  present  time  it 
occurs  as  a  weed  in  nearly  all  arable  parts  of 
Europe  and  Asia,  except  the  colder  regions. 
In  England  and  northern  Europe  it  is  only  an 
occasional  weed  along  roadsides  and  in  waste 
places,  and  is  not  troublesome  to  the  culti- 
vator. 

Prickly  lettuce  made  its  advent  in  this 
country  not  far  from  thirty-five  years  ago ; 
the  exact  date  and  place  have  not  yet  been 
ascertained.  It  is  supposed  to  have  come  in 
with  packing,  ballast  and  other  wastage.  So 
far  as  can  be  inferred  from  available  data,  the 
plant  gained  a  foothold  in  some  Atlantic  port. 
After  having  become  established  it  was  car- 
ried to  the  larger  cities  of  the  West,  and  from 
them  scattered  in  all  directions  by  the  rail- 


LIVING  PLANTS 


roads.     To  be  more  specific,  it  appears  to 

have  first  been  seen  in  Cambridge,    Mass., 

First  appear-     about  1863,   and  about    fifteen    or    twenty 

ance  in  years  later  to  have  appeared  in  several  of  the 

America  larger  cities  along  the  great  lakes  and  the 

Mississippi  river.    It  is  probable  that  the  fact 

that  these  cities  are  upon  water-v^ays  had 

little  to  do  with  the  matter,  but  being  great 

railway  centers  must  have  been  an  important 

factor. 

The  earliest  record  in  American  literature  is 
in  the  edition  of  Gray's  Manual  of  Botany 
issued  in  the  year  1867,  where  the  plant  is 
said  to  occur  in  waste  ground  and  along  road- 
sides in  Cambridge,  Mass.  In  the  editions  of 
1866  and  earlier  it  is  not  mentioned.  It  was, 
however,  to  be  found  in  Cambridge  at  least 
four  years  earlier  than  the  published  record, 
as  specimens  exist  in  the  Gray  Herbarium  of 
Harvard  University,  collected  by  Mr.  D.  Mur- 
ray, in  both  1863  and  1864.  It  was  found 
upon  ballast  ground  near  New  York  City  in 
1879,  but  not  seen  in  previous  years.  The 
ballast  grounds  of  Philadelphia,  which  have 
received  much  attention  from  local  botanists, 
do  not  appear  to  have  yielded  a  specimen  of 
the  plant  until  1883.  Along  the  Atlantic  sea- 
board the  plant  is  still  comparatively  uncom- 
mon, and  does  not  become  an  abundant  weed 


WILD  LETTUCE 


anywhere  in  the  region  east  of  the  Alleghany 
mountains. 

Although  the  plant  did  not  find  an  especial- 
ly congenial  soil  and  climate  when  it  landed 
upon  our  shores  in  its  emigration  venture, 
yet  it  was  able  to  maintain  itself  and  to 
spread.  In  the  course  of  fifteen  years  it  had 
penetrated  into  the  Mississippi  valley,  prob- 
ably making  the  longer  distances  as  the  hobo 
travels,  by  clinging  to  freight  trains,  for  it  is 
first  recorded  as  seen  in  St.  Louis  in  1877.  It 
was  afterward  detected  in  Toledo,  Chicago, 
St.  Paul  and  other  cities.      In  three  or  four 


~~~~~>---i^  w 

ttt 

k 

m^ 

^ 

t^^s 

V]?3^ 

P 

^Y 

1\\ 

^'\i 

/" 

^ 

Fig.  4. — Map  of  the  distribution  of  wild  lettuce,  as  reported 
to  the  U.  S.  Department  of  Agriculture  up  to  October,  1895. 
The  comparative  rarity  of  the  weed  in  the  Atlantic  states, 
where  first  introduced,  and  its  abundance  in  the  central  states, 
are  conspicuously  shown.     (After  Dewey.) 

years  it  was  an  abundant  weed  in  almost 
every  large  city  of  the  central  west.    At  the 


Fifteen  years 
of  conquest 


LIVING  PLANTS 


present  time  it  is  especially  abundant  in  this 
part  of  the  country,  not  only  in  cities  and 
towns,  but  on  farm  lands  and  along  high- 
ways. 

The  inference  appears  well  founded  that  the 
plant  has  found  its  most  congenial  domain 
between  the  Alleghany  and  Rocky  mountains, 
and  between  the  fortieth  and  forty-third  par- 
allels. The  region  in  which  it  has  become  so 
w^ell  established  and  so  abundant  as  to  take 
on  the  character  of  a  prominent  weed  em- 
braces the  northern  half  of  the  states  of  Ohio, 
Indiana,  Illinois,  the  southern  parts  of  Mich- 
igan and  Wisconsin,  and  part  of  Iowa.  Out- 
side of  this  region  it  occurs  locally  in  every 
direction  so  that  its  distribution  may  now  be 
said  in  general  to  extend  throughout  the 
United  States. 

Probably  no  one  thing  about  this  plant  im- 
presses the  observer  more  that  the  appear- 
ance of  having  "come  to  stay,"  an  expression 
used  by  many  of  those  who  have  recorded 
their  first  acquaintance  with  it.  It  is  a  weed 
not  only  because  it  is  a  "plant  out  of  place," 
but  because  it  possesses  certain  attributes 
that  enable  it  to  maintain  itself  wherever  a 
seed  finds  moisture  and  soil  enough  for  the 
forthcoming  plantlet  to  gain  a  foothold. 

Before  discussing  this  pre-eminent  trait  of 
the  plant,  however,  it  will  be  well  to  mention 


WILD  LETTUCE 


some  lesser  features  that  go  to  help  it  in  its 
conquest  of  the  land.  In  this  connection  the 
number  and  ease  of  distribution  of  its  seeds  is 
an  important  item.  Each  small  head  of  flow-  ^^^  ^^^  ^j^^,^ 
ers  ripens  about  twelve  seeds  (/.  e.  seed-like  distribution 
fruits),  and  a  plant  of  medium  size,  according 
to  an  estimate  made  by  Miss  Freda  Detmers, 
bears  688  heads,  or  8,526  seeds.  Each  seed  is 
well  constructed  and  protected  to  enable  it  to 
withstand  a  siege  of  the  elements,  and  is  like- 
ly to  reach  the  succeeding  springtime  in  good 
germinatingcondition,  unless  devoured  by  the 
birds.  This  contingency  is  not,  however,  of 
much  moment,  for  the  seeds  are  enclosed  by  a 
close  wrapping  of  green  scales  until  entirely 
ripe;  they  are  then  fully  exposed  only  a  short 
time,  being  carried  away  by  the  first  breeze; 
and  when  they  drop  to  the  ground,  after  a 
longer  or  shorter  sail  through  the  air,  they 
become  almost  invisible,  their  color  being  that 
of  dry  soil. 

Each  seed,  as  it  leaves  the  mother  plant,  is 
supported  from  a  white,  feathery  parachute, 
about  half  an  inch  across,  which  enables  it  to 
keep  afloat  upon  currents  of  air  for  a  long 
time,  and  ensures  the  plant  a  wide  and  rapid 
dissemination. 

The  flowers,  which  are  yellow  and  small, 
only  open  a  short  time  on  clear  days,  and 
then  close  until  the  seed  is  ripe,  and  in  the 


LIVING  PLANTS 


meantime  look  almost  like  3'oung,  unopened 
buds.  This  deceptive  appearance  may  lead 
the  cultivator  to  think  he  is  cutting  the  v^eed 
in  the  bud  before  it  has  blossomed,  when  in 
reality  it  is  loaded  with  young  seeds,  which 
will  ripen  as  the  plant  dies,  and  be  discharged 
to  start  another  crop,  almost  as  effectively  as 
if  the  plant  had  been  left  standing. 

The  plant  finds  protection  from  herbivorous 
animals  and  boring  insects  through  its  bitter 
milky  juice.  For  although  like'  the  garden 
lettuce,  it  is  tender  and  palatable  when  young, 
it  becomes  exceedingly  disagreeable  to  the 
taste  after  the  flower  stalks  start  up. 

The  prickles  also,  although  weak  and  not 
very  abundant,  have  a  protective  value  to  the 
plant  by  restraining  animals  from  eating  it. 

Although  the  plant,  by  its  milky  and  bitter 
How  to  be  juice,  and  by  its  prickles,  renders  itself  dis- 

a  successtu  tasteful  and  unattractive  as  food  for  animals, 

and  by  prodigality  of  seeds,  with  their  ample 
means  for  distribution  and  self-protection,  in- 
sures a  rapid  and  wide  dissemination,  thereby 
securing  great  advantages  as  a  dominant  and 
ever-present  member  of  every  area  of  vegeta- 
tion, yet  it  is  the  possessor  of  another  attri- 
bute belonging  to  a  successful  weed  of  even 
more  importance,  and  that  is  its  ability  to 
grow  and  seed  whatever  the  character  of  the 
soil  and  surroundings.     Stone  heaps,  weed- 


WILD  LETTUCE 


choked  corners  of  fences  and  yards,  alongside 
gutters  and  roadways,  a  crevice  in  the  pave- 
ment, beaten  paths,  all  are  acceptable  places 
in  which  to  flourish.  But  such  poverty  and 
ill  usage  are  by  no  means  essential  factors  in 
its  success,  for  it  also  springs  up  in  meadows, 
gardens  and  cultivated  fields.  Still  the  power 
to  extract  sufficient  moisture  and  food  from 
compacted  and  sun-beaten  earth,  and  thus  to 
overtop  competitors,  and  in  the  less  favorable 
spots  to  grow  where  few  plants  could  live, 
place  it  in  the  first  rank  of  noxious  annual 
weeds. 

Where  it  can  maintain  life,  seed  will  be 
formed,  even  when  conditions  are  unfavor- 
able for  full  development.  Thus  one  will 
often  find  in  very  dry  soil  plants  only  a  few 
inches  high  bearing  a  number  of  flower  heads 
and  fully  formed  seeds.  If  by  any  accident 
the  upper  part  of  the  plant  is  removed, 
branches  at  once  start  from  below,  and  bear 
leaves  and  flowers. 

The  tenacious  hold  upon  life  which  the  wild 
lettuce  exhibits  is  remarkable.  It  may  be 
broken  down,  trod  upon,  cut  off",  and  yet  it 
puts  out  new  shoots  from  below  and  flourishes 
again  ;  its  roots  may  be  in  the  driest  gravel, 
the  most  compact  clay,  or  squeezed  into  the 
crevices  of  walls  or  pavements  where  moisture 
almost  fails,  and  yet  it  grows.    But  all  this 


LIVING  PLANTS 


tenacity  of  life  is  only  displaj'ed  as  long  as 
the  roots  remain  undisturbed.  A  plant  of 
wild  lettuce  once  pulled  up  dies  as  quickly  as 
any  other  plant.  When  mowed,  the  top  that 
is  cut  off  dies  as  soon  as  ragweed,  cocklebur, 
horseweed  or  thistles  do ;  it  possesses  none  of 
the  live-for-ever  quality  of  purslane.  Neither 
has  the  root  any  recuperative  force  in  itself. 
If  the  stem  be  cut  away  well  down  into  the 
root,  the  whole  plant  dies,  no  shoots  ever 
starting  up  from  the  roots  in  the  soil. 

The  various  characteristics  enumerated 
largely  explain  the  success  of  the  plant  as  an 
introduced  weed.  In  the  central  west,  it  is  a 
formidable  rival  of  ragweed,  horseweed, 
cocklebur,  jimsonweed,  pigweed  and  other 
tall-growing  annual  weeds,  especially  during 
dry  seasons.  In  July  and  August  the  plant 
becomes  most  obnoxious,  for  then  it  sends  up 
the  seed  stalks.  The  heat  and  dryness  which 
are  likely  to  occur  at  this  season  and  retard 
the  growth  of  other  plants,  killing  the  small 
and  weak  ones,  give  the  conditions  which 
enable  wild  lettuce  to  gain  the  master3^  and 
flourish  in  disheartening  luxuriance. 

Not  only  has  the  plant  the  properties  of  a 
weed,  but  it  has  the  appearance  of  one.  It 
looks  weedy.  There  is  nothing  about  it  that 
will  ever  give  it  an  aesthetic  value.  To  cit}'- 
bred  and  country-bred  observers  alike  it  will 


WILD  LETTUCE 


be  only  a  weed,  and  nothing  of  the  nature  of 
the  transformation  of  ox-eye  daisies  into 
marguerites  will  ever  befall  it. 

Although  wild  lettuce  is  an  uncompromising 
weed,  with  no  beauty  of  flower  or  leaf,  yet  it 
possesses  some  points  of  much  interest  to  the 
student  of  plant  life.  "A  garden  in  which 
nothing  thrives  has  charms  that  soothe  the 
rich  possessor,"  asserts  Cowper;  and  if  we 
turn  in  such  a  spirit  of  expectancy  to  this 
weed  tramp,  although  annoying  us  by  its  un- 
welcome presence  in  our  yards  and  fields,  we 
will  find  it  to  have  characteristics  worthy  of 
study. 

The  mechanical  and  biological  causes  which 
determine  the  time  and  manner  of  opening 
and  closing  of  the  flower  heads  must  be  a  fer- 
tile subject  of  inquiry.  The  construction  and 
expansion  of  the  airy  parachute  also  deserves 
attention.  Numerous  other  things  about  the 
plant  may  well  engage  the  scrutiny  of  the 
careful  student. 

Only  one  of  these  features  need  occupy  us  at 
the  present  time,  however.  The  species  is 
characterized  in  the  various  manuals  as  pos- 
sessing vertical  leaves.  As  nearly  all  plants 
hold  their  leaves  horizontal,  i.  e.,  with  the 
edges  right  and  left,  this  peculiarity  of  the 
edges  of  the  leaves  being  presented  up  and 
down,  that  is,  at  right  angles  to  the  custom- 


LIVING  PLANTS 


ary  position,  may  repay  closer  examination. 
A  little  scrutiny  shows  that  the  leaf  is  set 
upon  the  stem  in  the  normal  manner,  and  the 
vertical  position  attained  by  a  quarter  turn 
near  the  base.  Some  leaves  turn  one  way, 
and  some  the  opposite  way,  to  gain  the  de- 
sired uprightness. 

This  in  itself  is  odd  enough,  but  a  further 
examination  shows  all  the  leaves  on  a  plant 
to  stand  for  the  most  part  in  one  plane.  If 
the  plant  is  looked  at  from  a  certain  point  of 
view,  one  sees  the  flat  surfaces  of  the  leaves, 
partly  upper  and  partly  under  surfaces,  while 
seen  at  right  angles  to  the  former  direction 
the  leaves  present  their  edges  only.  The 
leaves  of  each  plant,  in  fact,  lie  approximate- 
ly in  a  single  plane. 

Even  stranger  yet,  the  plane  in  v^rhich  the 
leaves  lie  is  that  of  the  meridian,  that  is,  the 
leaves  of  the  prickly  lettuce  present  their 
edges  north  and  south.  The  species,  in  fact, 
is  a  so-called  compass  plant,  and  exhibits  one 
of  the  most  curious  and  interesting  cases  of 
physiological  adaptation  to  be  met  with  in 
plants.  Its  polarity  was  first  observed  by 
Dr.  Stahl,  professor  of  botany  at  Jena,  who 
published  a  very  full  account  of  the  matter 
in  1881. 

There  are  two  species  known  which  are  pre- 
eminently entitled  to  be  called  compass  plants: 


WILD  LETTUCE 


one  is  the  subject  of  this  article,  the  prickly 
lettuce,  a  native  of  the  old  world,  the  other  is 
the  rosin  weed,  which  is  indigenous  to  the 
new  world.  The  latter  (Silphium  lacinatum 
L.)  occurs  on  the  western  prairies  from  Ohio 
to  the  Rocky  mountains.  It  is  a  large,  coarse 
plant,  but  yet  an  attractive  one,  with  sun- 
flower-like heads.  It  is  usually  known  as 
rosin  weed,  from  the  resinous  exudation, 
which  children  gather  and  convert  into  a 
white  palatable  chewing-gum. 

So  strong  isthepolarity  of  the  leaves  of  this 
plant  that  it  has  repeatedly  served  a  very 
useful  purpose  in  providing  travelers  with 
their  bearings  when  lost  on  the  prairies  during 
dark  nights  or  cloudy  days.  This  character- 
istic was  familiar  to  pioneers  long  before  Gen. 
Alvord  of  the  U.  S.  Army  made  it  known  to 
the  scientific  world  in  1842.  Longfellow, 
upon  hearing  of  the  plant  and  its  service  to 
travelers,  made  it  the  basis  of  some  lines  in 
Evangeline : 

"Look  at  this  vigorous  plant  that  lifts  its  head  from 

the  meadow, 
See  how  its  leaves  are  turned  to  the  north,  as  true  as 

the  magnet ; 
This  is  the  compass  flower,  that  the  finger  of  God  has 

planted 
Here  in  the  houseless  wild,  to  direct  the  traveler's  jour- 
Over  the  sea-like,  pathless,  limitless  waste  of  the  des- 
ert." 

Unfortunately  the  poet  at  first  misappre- 
hended the  real  character  of  the  plant,  with 


LIVING  PLANTS 


its  coarse,  rigid  stem,  and  wrote,  "Look  at 
this  delicate  /lower  *  *  *  that  the  finger  of 
God  has  suspended  here  on  its  fragile  stalk,' ^ 
but  in  later  editions  of  the  poem  changed  the 
wording  as  above. 

The  compass  plant  of  the  prairies  and  the 
compass  plant  of  the  highways  differ,  in  that 
the  former  exhibits  polaritj'^  chiefly  in  the  rad- 
ical leaves  (large,  coarse  leaves,  a  foot  or  two 
long),  and  the  latter  in  the  stem  leaves. 
Otherwise  the  phenomenon  in  the  two  plants 
is  practically  identical. 

There  was  much  conjecture  for  a  long  time 
as  to  the  cause  of  this  unique  behavior.  It 
Explanation  ^^^g  suggested  that  the  magnetic  currents  of 
° -*rti^  '  the  earth  acted  upon  iron  oxide  in  the  leaves, 
or  that  the  abundant  resin  in  the  plant 
brought  about  electrical  disturbances.  But 
both  theories  failed  when  put  to  the  test,  and 
others  stood  no  better  until  the  relation  to 
light  was  observed.  It  was  found  that  plants 
grown  in  boxes,  if  turned  one  quarter  round, 
readjusted  their  leaves  to  again  point  north 
and  south.  This  occurred  when  the  plants 
were  grown  in  bright  light,  but  not  when 
grown  in  darkness.  It  was  also  found  that 
the  number  of  stomata  (breathing pores)  was 
essentially  the  same  on  both  surfaces  of  the 
leaf,  while  ordinarily  there  are  very  many 
more  below  than  above.    Further  uniformity 


iar  trait 


WILD  LETTUCE 


of  structure  between  the  two  sides  of  the  leaf 
was  also  found  to  exist. 

It  is  unnecessary  to  point  out  all  the  rea- 
sons for  the  conclusion  finally  reached,  that 
compass  plants  are  endowed  with  an  organi- 
zation which  enables  the  leaves,  as  the  mid- 
day sun  becomes  unpleasantly  bright,  to  turn 
part  way  around  and  present  less  surface  to 
the  action  of  its  rays.  Figuratively,  one 
might  say  the  plant  turns  a  cold  shoulder  to 
the  sun,  when  he  becomes  too  ardent. 

Ordinary  leaves  permit  the  sun  to  shine  up- 
on the  upper  surface  only,  having  that  side 
constructed  to  bear  the  light  and  heat  with- 
out injury,  while  the  under  side,  having  a 
more  delicate  organization,  is  turned  from  the 
sun.  When  the  compass  plant  adjusts  its 
leaves  in  the  only  position  possible  by  which 
equal  illumination  is  secured  for  the  two  sides 
during  the  middle  of  the  day,  the  under  side 
of  the  leaf  is  evidently  in  danger  of  injury  un- 
less reorganized.  Such  a  change  does  in  fact 
come  about.  As  the  palm  of  the  hand  is  cal- 
loused by  repeated  rough  usage,  so  the  lower 
surface  of  the  leaf  is  inured  to  the  sun's  action 
by  exposure,  the  change  consisting  of  a  pro- 
found alteration  of  the  underlying  tissues  as 
well  as  of  the  superficial  portion.  Physiolog- 
ically there  is  no  longer  an  upper  and  a  lower 
surface  to  the  meridional  leaf,  but  simply  a 


LIVING  PLANTS 


right  and  a  left  surface;  both  sides  function 
alike. 

Sometime  ago  the  writer  made  the  obser- 
vation that  the  garden  lettuce  also  shows 
polarity  of  the  stem  leaves,  although  not  so 
marked  as  in  the  wild  plant.  It  is  stronger  in 
the  plain  narrow  leaves  of  the  Cos  and  Deer- 
tongue  varieties  than  in  the  curled  leaves  of 
the  more  common  varieties. 

Both  the  wild  and  garden  forms  show  no 
vertical  adjustments  of  the  basal  or  so-called 
root  leaves,  the  edible  part  of  the  cultivated 
plant.  In  feral  plants  these  leaves  are  not 
called  upon  to  endure  the  hot  sun  of  July  and 
August,  having  already  performed  their  office 
during  spring  and  early  summer,  and  died. 
The  compass  plant  of  the  prairies  (Silphium), 
on  the  contrary,  retains  its  root  leaves 
throughout  the  torrid  season.  It  is  evident 
that  the  device  is  primarily  a  midsummer  ad- 
justment, only  developed  in  such  foliar  organs 
as  are  destined  to  endure  the  fiercest  insola- 
tion. 

There  are  eight  or  nine  species  of  wild  let- 
tuce indigenous  to  North  America,  but  none 
of  them  has  yet  been  observed  to  show  po- 
larity. The  species  that  are  most  at  home  in 
the  western  prairie  regions,  such  as  Lnctuca 
Ludoviciana,  are  most  likely  to  show  tendency 
toward  the  habit. 


IV. 


mimosa:  a  typical  sensitive  plant. 


Uses 


Movement  as  an  adjustment  to  variations 
in  temperature  and  light  is  one  of  the  most 
necessary  and  most  highly  useful  adaptations 
made  by  leaves.  The  species  that  can  accom- 
plish the  movements  most  economically  will  ofmovement 
have  a  great  advantage  in  the  struggle  for 
existence  where  the  solar  factors  are  most  in- 
tense. In  fact  it  is  to  be  said  that  no  plant  in 
the  tropics  exposes  its  leaves  to  the  perpen- 
dicular rays  of  the  noonday  sun.  In  the 
species  incapable  of  producing  the  movement, 
the  adjustment  is  secured  less  perfectly  by  the 
passive  drooping  of  the  leaves.  In  the  tem- 
perate zone  active  movements  of  leaves  are 
exhibited  by  species  of  Leguminosas,  Oxalidae, 
Malvaceae,  Tiliaceee  andMarsiliaceaeonl3',but 
in  the  tropics  the  number  is  enormously  mul- 

*Adapted   from  a  lecture  on  "Movements  of  Plants"  g^iven 
belore  the  Institute  of  Jamaica,  June  19,  1897. 


LIVING  PLANTS 


Power 

of  movement 


Characteristics 
of  mimosa 


ti plied  and  includes  among  other  families  the 
Euphorbiaceae  and  Marantaceae.  The  groups 
mentioned  have  shown  a  peculiar  fitness  for 
tropical  environment.  One  genus  alone, 
Cassia,  includes  four  hundred  and  fifty  species, 
nearly  all  of  w^hich  are  at  home  in  countries 
near  the  equator.  One  of  the  northern  repre- 
sentatives. Cassia  chamascrista,  has  acquired 
the  name  of  the  "Wild  Sensitive  Plant" 
throughout  the  middle  and  northern  states, 
while  Cassia  nictitans  is  similarly  designated 
in  New  England.  Southward  the  number  of 
species  increases  with  that  of  the  other  legum- 
inous plants  until  near  the  equator,  represen- 
tatives of  the  group  form  a  very  large  propor- 
tion of  the  total  mass  of  vegetation. 

Mimosa  padica  the  "Sensitive  Plant"  or 
"Shameweed"  of  the  West  Indies  is  one  of 
the  most  attractive  members  of  this  group, 
since  in  addition  to  the  typical  adjustments  of 
the  leaves,  which  it  performs  with  great  ra- 
pidity and  delicacy,  it  also  exhibits  reactions 
to  other  and  unusual  stimuli.  The  move- 
ments of  plants  are  generally  so  slowly  made 
as  to  be  incapable  of  detection  except  by  re- 
peated or  long  continued  observation.  Mi- 
mosa, however,  is  one  of  the  small  number 
which  is  capable  of  rapid  movement  of  large 
organs.  This  fact,  and  the  great  degree  of  ir- 
ritabilitv  shown,  drew  the  attention  of  the 


earlier  botanists,  and  it  has  been  the  object 
of  a  succession  of  investigations  for  more 
than  a  century.  The  plant  has  become  a 
classical  illustration  in  botanical  literature, 
and  a  drawing  showing  positions  taken  by 
the  leaves  after  movement,  made  by  Duchar- 
tre  many  years  ago,  is  still  reproduced  in  text 
books. 

The  equatorial  zone  is  the  home  of  an  enor- 
mous number  of  species.  The  island  of  Ja- 
maica, with  an  area  of  about  6,000  square 
miles,  about  that  of  Connecticut,  furnishes 
approximately  four-fifths  as  many  species  of 
flowering  plants  as  are  to  be  found  in  the 
United  States  east  of  the  Mississippi  river. 
The  advent  of  modern  man  into  the  teeming 
tropical  areas,  and  the  facilities  he  afforded 
intentionally  and  unintentionally  for  distri- 
bution has  led  to  a  wholesale  emigration  and 
intermingling  of  tropical  forms. 

Mimosa  pudica  was  originally  an  inhabi- 
tant of  the  plains  of  Brazil  and  Venezuela,  but 
it  has  accompanied  man  in  his  journeys 
around  the  world  in  the  equatorial  regions. 
It  has  become  a  virile  pest  in  fields,  gardens 
and  pastures  in  warm  countries,  and  is  culti- 
vated in  greenhouses  in  latitudes  as  high  as 
55°  N. 

It  is  a  low,  spreading,  prostrate,  woody 
plant  in  the  tropics.   The  forms  seen  in  north- 


LIVING  PLANTS 


Ofganization 


ern  greenhouses  show  an  erect  stem  because 
of  insufficient  light  and  are  "drawn"  in  the 
language  of  the  gardener.  The  scattered 
leaves  consist  of  a  long  petiole  bearing  two 
or  four  leaflets,  which  are  divided  into  eight 
to  twelve  pairs  of  small  ovate  pinnules.  The 
bases  of  the  stalks  of  the  pinnules,  the  leaflets 
and  the  petiole  are  developed  in  the  form  of 
thick  cylindrical  swelhngs  (pulvini).  The 
woody,  mechanical  tissue  in  the  stalks  is  in 
the  form  of  a  hollow  cylinder,  but  in  passing 
through  thepulvinusto  join  the  stem  it  comes 
together  forming  a  solid  rod.  The  central 
cylinder  of  mechanical  tissue  is  surrounded  by 
a  thick  layer  of  thin  walled  motile  cells  which 
are  capable  of  rapid  changes  in  form.  Such 
alterations  are  due  to  variations  in  the  hydro- 
static pressure  in  the  cells.  When  the  cells  of 
one  side  of  the  pulvinus  give  off"  water  which 
passes  into  the  spaces  between  the  cells,  a 
curvature  toward  this  side  results  from  the 
unchanged  pressure  of  the  turgid  cells  of  the 
opposite  side.  The  sinking  of  a  leaf  upon  its 
petiole  is  due  to  the  relaxation  of  the  cells  of 
the  lower  side  of  the  pulvinus.  When  these  cells 
reabsorb  the  water  from  the  intercellular 
spaces,  their  former  size  and  shape  is  slowly 
regained  and  the  leaf  is  returned  to  its  former 
position. 


The  continuous  observation  of  half  a  dozen 
healthy  plants  through  the  course  of  a  mid- 
summer's day  will  reveal  the  greater  number 
of  reactions  exhibited  by  this  plant. 

Early  in  the  morning  the  pinnules  are  seen 
to  occupy  a  horizontal  position  with  the 
blades  fully  exposed  to  the  light.  The  petioles 
are  slightly  elevated  above  the  horizontal. 
As  the  sun  mounts  toward  the  noonday  posi- 
tion its  rays  increavse  in  intensity,  and  their  ef- 
fect on  horizontal  leaf-blades  will  increase  cor- 
respondingl3^  At  sometime,  however,  before 
the  rays  strike  the  surface  perpendicularly,  the 
regulatory  mechanism  of  the  plant  sets  up 
movements  in  the  pinnules  by  which  their 
surfaces  are  directed  upward  at  an  acute 
angle.  The  angle  increases  as  the  sun  nears 
and  passes  the  zenith  until  the  edges  of  the 
blades  are  directed  almost  exactly  toward 
the  sun,  and  its  rays  exercise  an  actvial  effect 
on  the  leaf  not  much  greater  than  in  the 
early  forenoon.  If  this  adaptation  were  not 
made,  the  fierce  rays  would  strike  through 
the  leaf-blades  so  strongly  as  to  injure  the 
chlorophyll  and  evaporate  more  water  than 
could  be  supplied  by  the  roots,  thus  causing 
wilting. 

As  the  sun  declines  toward  the  west,  the 
blades  return  once  more  to  the  horizontal 
position,  but  the  approach  of  night  brings 


Day  positions 
of  leaves 


Night  positions 
of  leaves 


LIVING  PLANTS 


Fig.  5:— Mimosa:     AA,  normal  position  ;  BB,  night 
position  ;   CC,  position  after  shock. 


another  danger  to  the  plant,  consisting  in  an 
extremely  rapid  radiation  of  heat  and  accom- 
panying loss  of  water.  This  threatened  in- 
jury is  again  avoided  by  deflection  of  the 
blades  from  the  horizontal  to  the  perpen- 
dicular. The  movement  begins  at  or  near 
sunset  and  the  lamina  slowly  rise  until  their 
upper  surfaces  are  appressed.  The  evapora- 
ting surface  is  thus  reduced  exactly  one-half, 
while  the  radiation  of  heat  is  much  less  from 
a  vertical  plane  than  a  horizontal  one.  Ref- 
erence to  the  accompanying  illustrations  will 
show  that  minor  movements  have  occurred. 
A  movement  of  the  pulvinus  at  the  base  of  the 
petiole  results  in  placing  that  member  hori- 
zontally. 

''or  nyctitropic  move- 
ments occur  daily  while 
those  to  avoid  the  ef- 
fects of  the  hot  sun  are 
exhibited  only  when  a 
certain  intensity  is  at- 
tained. The  regular 
daily  recurrence  of  the 
conditions  which  cause 
the  nyctitropic  move- 
ments has  fixed  them 
so  firmly  in  the  plant 
-- \  thatthey   occur  at 

^"'-  ^•7f"Mimo"i'°''"°"       rhythmic  intervals  re- 


The  "night,"  "sleep' 


Reaction 
to  shock,  etc. 


LIVING  PLANTS 


gardless  of  the  surroundings  of  the  plant. 
The  "sleep"  of  the  plant  on  any  given  night 
is  not  the  direct  result  of  the  absence  of  light 
at  that  time  but  of  the  darkness  of  previous 
nights.  If  a  healthy  individual  is  placed  in 
continuous  Hght  or  darkness,  it  continues  to 
"go  to  sleep"  at  regular  intervals  for  several 
days,  but  finally  sickens  or  adjusts  itself  to 
the  new  conditions  imposed  upon  it.  The 
habit  is  regained  on  restoration  to  normal 
conditions. 

The  sleep  position  may  be  produced  in  the 
middle  of  the  day  by  suddenly  excluding  the 
sun's  rays,  but  the  normal  position  will  soon 
be  regained  unless  the  temperature  is  greatly 
reduced.  Mimosa  is  one  of  the  plants  in 
which  the  night  position  is  wholly  a  response 
to  low  temperatures. 

If  a  screened  plant  is  suddenly  exposed  to 
the  sun's  glare  in  the  middle  of  the  day,  the 
leaves  sink  and  the  pinnules  close  as  if  struck 
or  jarred.  Many  interesting  deviations  from 
these  typical  reactions  have  been  observed. 
Thus,  if  a  healthy  plant  is  placed  in  a  dry 
room  at  15°  Centigrade  the  blades  will  be 
found  extended  in  the  morning,  while  the  pe- 
tioles have  assumed  and  retained  a  depressed 
position.  The  reactions  described  above  are 
not  especially  characteristic  of  mimosa,  since 
they  are  exhibited  by  many  hundreds  of  spe- 


cies  and  may  be  easily  observed  in  the  bean, 
oxalis,  locust,  cassia,  and  other  leguminous 
species. 

It  has  other  forms  of  irritability,  not  at  all 
common  or  widely  distributed.  Thus  if  one 
should  lightly  touch,  or  blow  the  breath  upon, 
the  expanded  leaflets  of  mimosa  at  ordinary 
temperatures,  the  pinnules  or  ultimate  divi- 
sions of  the  leaf  would  rise  up  above  the  mid- 
ribs upon  which  they  are  borne,  closing  in 
pairs.  If  the  shock  were  given  with  sufficient 
force  or  if  a  blow  of  the  pencil  be  given  ujion 
the  stem  all  the  leaves  will  erect  the  pinnules 
and  sink  on  the  petioles.  A  flame  held  near 
the  leaflet,  or  the  fumes  of  acid,  ammonia,  or 
chloroform,  will  cause  the  movement  also, 
while  an  electric  current  applied  to  almost 
any  part  of  the  plant  has  a  similar  effect. 
More  correctly  speaking,  the  breaking  of  the 
current  is  the  true  stimulus.  The  plant  re- 
sponds to  chemical,  mechanical,  thermal 
and  electrical  stimuli.  An  interesting  differ- 
ence between  the  reactions  of  mimosa  and 
those  of  the  tendrils  of  climbing  plants  is  that 
the  latter  move  when  pressed  by  a  solid  body, 
but  not  when  struck.  Mimosa,  on  the  other 
hand,  responds  to  a  blow  or  shock,  but  not  to 
a  steady  pressure,  as  the  leaves  may  be  given 
a  steady  pressure  by  the  thumb  and  finger 
without  results. 


LIVING  PLANTS 


A  careful  analysis 
of  the  above  reac- 
tions will  yield  many 
interesting  re s  u  1 1  s. 
If  a  quick  snip  is  giv- 
en with  scissors 
to  the  terminal 
pair  of  pinnules 
in  one  of  the  upper 
leaves,  the  pinnules 
disturbed  will  close 
rapidly  and  then  the 
other  pairs  will  react 
in  succession  until 
the  base  of  the  leaflet 
is  reached.  After  a 
short  interval  the 
basal  pairs  of  pin- 
nules of  the  neigh- 
boring leaflets  close 
and  thepairs  toward 
the  apices  in  succes- 
sion. Before  the  mo- 
tion has  been  taken 
up  by  all  of  the  leaf- 
lets the  pulvinus  at 
the    base    of    the 

Fig.  7. — Successive  positions  of  mimosa  after  stimulation  at 
the  tip  of  a  leaflet,  a,  position  a  few  seconds  after  a  flame  is 
applied  at/,  b,  the  impulse  has  reached  the  base  of  the  leaf, 
c,  the  impulse  has  traversed  nearly  the  entire  shoot  and  isnear- 
ing  the  leaf-tips  of  the  last  leaf  reached. 


main  leaf-stalk  acts,  and  the  entire  leaf 
sinks.  If  the  stimulus  has  been  given  with 
sufficient  force,  or  by  means  of  a  match  flame 
instead  of  the  forceps  or  scissors,  the  move- 
ment will  be  taken  up  in  turn  by  the  leaves 
above  and  below  the  one  treated.  The  reac- 
tion of  the  plant  is  most  rapid  in  specimens 
growing  vigorously,  and  standing  in  moist 
air  at  a  temperature  of  30-35°  centigrade. 

It  may  be  noticed  that  a  short  time  elapses 
between  the  action  of  the  stimulus  from  the 
scissors  or  flame  and  the  reaction  of  the  leaf- 
let. This  is  termed  the  latent  period  and 
amounts  to  slightly  less  or  more  than  a  sec- 
ond according  to  conditions.  The  experi-  Transmission 
ments  also  have  demonstrated  that  the  effects  °*  stimuli 
of  a  force  applied  to  one  part  of  the  plant 
may  be  transmitted  over  its  entire  body,  which 
is  often  a  yard  or  a  meter  in  length.  If  care- 
ful note  of  the  time  is  made  between  the  appli- 
cation of  the  stimulus  to  the  plant  and  the 
reactions  in  different  portions  of  the  plant, 
together  with  accurate  measurements,  it  will 
be  found  that  the  impulse  or  force  set  in  mo- 
tion by  the  stimulus  travels  at  the  rate  of 
eight  to  twenty-five  millimeters  (%  to  1  inch) 
per  second  under  favorable  circumstances. 

As  the  plant  stands  in  the  quiet  atmosphere 
on  a  warm  morning,  a  breath  of  air  or  the 
smallest  drops  of  water  striking  the  blades 


LIVING  PLANTS 


will  cause  reactions.  If  the  movement  of  the 
air  is  continuous  and  freshens  to  a  breeze,  or 
the  drops  of  water  are  followed  by  a  steady 
rain,  the  plant  finally  replaces  the  pinnules  in 
the  original  position,  though  blown  about  or 
beaten  by  the  rain.  The  plant  is  enabled  to  do 
this  by  its  great  power  of  accommodation  to 
any  force  acting  upon  it.  The  real  stimulus 
is  not  the  force  in  itself  but  consists  in  changes 
in  the  forces  acting  upon  the  plant.  This  may 
be  demonstrated  if  a  specimen  is  subjected  to 
a  spray  of  water  forming  an  artificial  rain- 
Repetition  storm  in  a  greenhouse.  After  a  time  it  be- 
of  stimuli  comes  accustomed  to  the  falling  water  and 
resumes  the  normal  position.  If  now  the 
force  of  the  spray  is  suddenly  increased,  a  re- 
action is  shown,  and  the  pinnules  are  closed. 
After  exposure  to  the  heavier  spray  for  a  time 
it  once  more  resumes  the  normal  attitude  and 
the  experiment  may  be  repeated  with  similar 
results.  A  specimen  of  mimosa  grown  in  a 
pot  may  be  carried  on  a  journey  in  a  wagon 
or  railroad  train,  and  may  be  seen  to  resume 
the  normal  position  after  it  has  become  accus- 
tomed to  the  jarring  from  the  vehicle,  if  the 
temperature  and  light  are  favorable.  While 
an  individual  may  thus  accommodate  itself 
to  an  unusual  intensity  of  any  force,  it  is  as 
delicately  sensitive  to  other  stimuli  as  usual. 
Thus  one  may  stand  some  distance  from  a 


plant   exposed    to  an  artificial  rainfall  and 
cause  a  reaction  by  a  puflf  of  the  breath. 

When  a  plant  has  become  accustomed  to  a 
continuously  acting  force,  the  amount  of  in- 
crease necessary  to  secure  a  reaction  is  a  defi- 
nite and  fixed  proportion  of  the  continuously 
acting  force.  The  formula  which  expresses 
this  proportion  has  been  found  to  apply  to 
the  reactions  of  both  plants  and  animals. 

The  manner  in  which  impulses  are  trans- 
mitted from  one  part  of  a  plant  to  another  Method 
forms  a  problem,  the  solution  of  which  has  of  transmission 
baffled  investigation  for  more  than  a  century. 
Many  interesting  experiments  looking  to- 
ward a  determination  of  the  question  have 
been  made. 

It  has  been  found  that  when  a  section  of  a 
stem  has  been  girdled  by  the  removal  of  the 
bark  and  cambium  the  transmission  of  an  im- 
pulse is  in  nowise  hindered,  thus  proving 
that  the  path  lies  through  the  wood,  which 
in  this  plant  is  composed  of  cells  which  die  on 
attaining  normal  size.  The  fact  is  proven 
more  positively  by  the  removal  of  the  wood 
from  another  section,  the  living  tissues  and 
bark  being  allowed  to  remain.  In  this  in- 
stance no  transmission  occurs. 

If  a  short  section  of  a  stem  is  killed  by 
means  of  a  bandage  of  cloth  kept  saturated 
with  boiling  water  for  several  minutes,  trans- 


LIVING  PLANTS 


mission  is  not  hindered  and  a  stem  may  be  so 
treated  as  to  consist  of  alternate  dead  and 
living  portions  and  still  transmit  the  effects 
of  stimulation.  This  set  of  experiments  dispos- 
es of  the  idea  that  the  transmission  of  impulses 
is  in  any  sense  a  function  of  living  matter  in 
mimosa. 

The  presence  of  a  system  of  elongated  cylin- 
drical cells  in  the  outer  part  of  the  woody  tis- 
sue, containing  glucosides  and  water  under 
pressure,  led  to  the  formulation  of  the  theory 
that  these  tubes  were  the  paths  of  transmis- 
sion and  that  impulses  consisted  of  simple  hy- 
drostatic disturbances  traversing  the  system, 
as  the  pulsations  of  the  forcing  engines  are 
transmitted  through  the  mains  and  pipes  of  a 
city  water  system. 

The  mere  presence  of  these  tubes  can  have 
no  especial  significance,  because  they  are  found 
in  hundreds  of  species  of  Leguminosai  in  which 
transmission  does  not  occur.  It  is  to  be  ad- 
mitted of  course  that  the  tubes  might  serve 
such  use  in  mimosa,  though  not  in  any  other 
plant.  When  sudden  disturbances  are  induced 
in  the  contents  of  the  tubes  by  means  of 
powerful  pumps,  abrupt  pressure,  the  appH- 
cation  of  heated  rods  to  the  stem  or  strong 
chemical  solutions  to  cut  surfaces,  no  reac- 
tions follow,  and  it  is  difficult  in  face  of  such 
results  to  maintain  that  an  impulse  is  a  hy- 


drostatic  disturbance.  As  a  matter  of  fact 
impulses  have  been  conducted  through  air-dry 
wood  of  the  stem  in  which  hydrostatic  trans- 
mission would  be  impossible,  and  the  only 
pathway  would  be  the  water  of  imbibition  in 
the  cell  wall.  Information  as  to  the  condi- 
tion of  water  in  the  wall  is  not  sufficient  to 
make  the  formulation  of  any  reasonable 
theory  based  on  this  assumption  possible. 

The  reaction  of     mimosa  to  impact  and 
injury  is  supposed  to  be  a  protection  against    Purpose 
drouth  and  damage  from  grazing  animals,    ^^'^^^^tion 
A  recent   writer  says:     "When   a  browsing    *° "^^^^^^ ^t^- 
animal  approaches  a  clump  of  mimosa  and 
agitates   any   part  of  it  at   all   strongly   the 
green  appearance  disappears  at  once,  and  only 
an   apparently  withered  clump  in  which  the 
hard  and  prickly  stems  are  most  conspicuous 
remains ;  the  consequence  being  that  the  ani- 
mal either  turns  away  or  passes  through  the 
clump  to  less  bewildering  pasturage." 

As  the  plant  has  not  been  studied  in  its 
habitat  in  Venezuela  and  Brazil  it  is  not 
definitely  known  whether  it  is  ravaged  by 
grazing  animals  or  not.  The  theory  was 
once  proposed  and  widely  reiterated  that  the 
contact  irritabihty  of  mimosa  was  developed 
as  a  protection  against  hailstorms,  regardless 
of  the  fact  that  the  plant  never  encounters 
such  dangers  in  the  torrid  zone.    As  has  been 


LIVING  PLANTS 


shown  it  is  not  a  protection  against  rain,  be- 
cause the  plant  soon  becomes  accustomed  to 
the  falHng  drops,  and  opens.  The  fact  that 
many  plants  of  the  temperate  zone,  among 
which  is  the  ordinary  locust  {Robinia  pseud- 
acacia),  exhibit  irritability  to  impact  leads  to 
the  suggestion  that  the  plant  must  be  very 
delicately  poised  to  be  able  to  avoid  the  dan- 
gers of  changes  in  temperature,  and  that  any 
shock  sets  the  protoplasmic  machinery  in 
motion. 

The  movements  of  mimosa  in  response  to 
the  action  of  ether,  chloroform  and  other  an- 
esthetics, as  well  as  electricity,  is  due  to  the 
direct  action  of  these  agents  on  the  motor  tis- 
sues. A  similar  instance  is  afforded  by  the 
action  of  changes  in  temperature  upon  ten- 
drils. 

Equipped  with  an  irritable  organization  of 
such  a  high  degree  of  complexity,  mimosa  can 
easily  hold  its  own  in  the  swarm  of  competing 
organisms  in  tropical  climates.  A  similar  or- 
ganization would  be  highly  disadvantageous 
as  well  as  impossible  in  high  latitudes. 


Unity 


UNIVERSALITY  OF   CONSCIOUSNESS   AND   PAIN' 

"It  is  my  faith  that  every  flower  that  blows 
Enjoys  the  air  it  breathes!" 

Wordsworth. 

It  is  the  glory  of  modern  science  to  have 
shown  that  the  phenomena  of  the  universe  are 
capable  of  being  grouped  into  classes  and  sub- 
classes, and  that  through  all  the  ramifications 
runs  an  essential  nexus,  or  genetic  association. 
In  the  organic  world  the  development  of  ^  nature 
plants  and  animals  has  been  shown  to  be 
governed  by  similar  laws  for  both,  and  their 
special  ways  of  maintaining  the  funderment- 
al  characteristics  of  their  existence  is  being 
found  more  and  more  to  be  based  upon  like 
properties. 

In  the  following  pages  the  writer  hopes  to 
present  a  generalization  that  throws  a  some- 
what different  light  upon  the  life  of  plants 

*Rcad  before  the  Parlor  Club,  an  organization  devoted  to 
literary  and  scientific  culture;  Lafayette,  Ind.,  Sept.  20,  1896. 


CONSCIOUSNESS  AND  PAIN 


Superstition 
of  the 
mandrake 


Can  a  man- 
drake feel? 


from  that  usually  entertained,  and  yet  he 
does  not  wish  to  claim  more  than  well-estab- 
lished facts  and  reasonable  analogy  wall  up- 
hold. 

An  old  superstition  ascribed  to  the  man- 
drake, a  common  plant  of  the  Mediterranean 
region,  a  supersensitireness  that  caused  it  to 
utter  such  cries  of  pain  when  drawn  from  the 
earth  "that  living  mortals,  hearing  them,  go 
mad."  This  marvelous  anthropomorphic  ex- 
hibition was  associated,  so  it  was  said,  with 
an  equally  marvelous  resemblance  of  the  plant 
to  a  human  body  wherein  lay  the  reasonable- 
ness of  the  plant's  behavior. 

By  logical  extension  of  modern  deductions 
regarding  the  nature  of  the  physical  basis  of 
life  and  the  unity  of  ecological  methods  in  its 
expression,  it  is  not  too  much  to'claim  that  a 
more  genuine  agreemeiit  exists  between  man- 
drakes and  man  than  the  superficial  one  of 
form  that  appealed  so  powerfully  to  the 
ancients;  in  fact,  as  is  well  known  at  present, 
the  representatives  of  both  kingdoms  not 
only  grow,  breath  and  require  food,  but  they 
respond  to  changes  in  environment  by  being 
irritable.  On  the  one  hand  the  irritability 
rises,  especially  among  the  higher  animals,  to 
a  clear  exhibition  of  feeling,  capable  of  induc- 
ing suffering ;  what  is  there  in  the  logic  of  the 
situation    that    prevents  us  from   assuming 


CONSCIOUSNESS  AND  PAIN 


that  plants  also  feel?  I  venture  to  say  that 
they  do  feel,  and  that  the  mandrake,  or  any 
other  plant,  is  really  hurt  when  pulled  forcibly 
from  the  ground,  suffering  its  modicum  of 
pain,  although  unaccompanied  by  signs  that 
make  the  fact  patent  to  our  senses.  If  a  plant 
can  feel  a  bodily  hurt,  it  must  necessarily  pos- 
sess consciousness,  for  pain  without  conscious- 
ness is  inconceivable.  Hence  the  thesis :  all 
living  organisms,  whether  animal  or  plant, 
are  capable  of  conscious  pain  to  a  degree  com- 
mensurate with  the  requirements  of  their 
nature. 

At  the  outset  it  must  be  clearly  recognized     ^     .       . 
that  the  word  consciousness,  as  used  in   this 


connection,  contains  no  reference  to  self-con- 
sciousness, which  implies  introspection.  Self- 
consciousness,  it  may  be  said  in  passing,  is 
necessary  that  the  individual  may,  for  in- 
stance, be  aware  of  its  own  identity,  or  may 
reflect  upon  a  given  sensation,  which  powers 
belong,  undoubtedly,  not  to  all  classes  of  be- 
ings, but  only  to  the  more  highly  organized, 
and  especially  to  those  with  a  centralized  ner- 
vous system. 

General  consciousness,  on  the  other  hand, 
implies  a  recognition  of  the  impact  of  stimuli; 
the  individual  knows  that  the  uniformity  of 
the  conditions  of  its  existence  is  disturbed, 
sometimes  pleasurably,  sometimes  painfully. 


consciousness 


LIVING  PLANTvS 


Examples  of 
consciousness 


Recognition  does  not  come,  however,  with  all 
changes  in  external  conditions,  they  must 
reach  a  certain  violence,  or  intensity,  before 
consciousness  is  aroused ;  and  the  degree  re- 
quired for  efficiency  will  vary  with  the  organ- 
ism. 

The  state  of  consciousness  and  the  usual 
accompanying  reaction  of  the  organism  can 
be  illustrated  by  the  well  known  effects  of  a 
thrust.  Let  us  suppose  that  the  organism  in 
question  is  a  man,  and  the  thrust  is  received 
from  the  proboscis  of  a  mosquito.  The  man 
may  be  especially  sensitive  to  mosquito  bites 
and  retaliate  with  a  violent  blow  of  the  hand. 
However,  being  a  rational  being,  he  may  first 
reflect  upon  the  probability  of  getting  the 
greatest  satisfaction  from  his  effort,  and  take 
certain  precautionary  measures  to  secure 
deadly  aim.  If  the  same  invasion  of  per- 
sonal rights  be  attempted  with  the  man's 
canine  companion,  the  reactionary  effects  are 
similar  in  every  essential ;  but  being  a  far  less 
rational  being  than  his  master,  the  dog  will 
give  little  or  no  thought  to  the  manner  of  the 
removal  of  the  oflending  insect.  As  we  go 
down  the  scale  of  organized  life  the  mosquito 
bite  will  continue  to  meet  with  counteraction, 
taking  on  more  and  more  the  character  of  a 
simple  sensitive  response  to  an  irritation. 


CONSCIOUSNESS  AND  PAIN 


In  order  to  carry  our  observation  further 
and  have  the  trials  under  better  control,  sup- 
pose a  splinter  of  wood,  or  a  feather,  be  used 
as  the  irritating  object.  If  now  thisawaken- 
er  of  consciousness  be  cautioush^  applied  to 
the  back  of  the  neck  of  an  unsuspecting  per- 
son, it  will  arouse  reaction,  provided  the  fric- 
tion has  been  sufficient  to  be  felt.  Suppose 
we  tickle  the  nose  of  a  dog,  who  is  taking  a 
siesta  with  his  eyes  shut;  there  is  not  sufficient 
difference  in  the  results  to  require  comment. 
If  the  back  of  a  caterpillar  or  worm  next  be 
tested,  a  wriggling  of  disapproval  takes 
place.  Now  touch  the  mantle  of  the  laz\^ 
clam,  and  make  sure  that  your  fingers arenot 
too  near  to  be  caught  between  the  jaws  of 
the  shell  as  it  springs  together.  Try  a  sea- 
anemone  and  watch  the  speedy  infolding  and 
packing  away  of  its  whole  garniture  of  bril- 
liant fringes.  Proceed,  if  you  choose,  to  the 
bell-animalcule,  the  amoeba,  and  others  of 
lowest  and  simplest  animals. 

But  we  need  not  stop  with  animals.  Try 
the  same  testontheleaf  of  the  Venus' fly-trap, 
and  note  the  astonishingly  quick  interlocking 
of  the  rat-trap  edges  of  the  leaf-blade,  a 
movement  that  has  brought  mortal  surprise 
to  many  a  fly.  Brush  the  inner  surface  of  a 
tendril  of  the  wild  cucumber  and  notice  how 
it  begins   in    a   moment   to   slowly'    coil   up. 


68  LIVING  PLANTS 

Touch  the  leaf  of  a  sensitive  plant  and  see  it 
shrink  away  into  the  smallest  compass  at- 
tainable. 

What  do  all  these  animal  and  plant  move- 
ments mean,  except  it  be  that  the  individual 
has  felt  something  and  acts  responsively,  ac- 
cording to  its  ability.  And  yet  it  may  be  ob- 
jected that  while  man  and  some  of  the  higher 
animals  may  possess  genuine  feeling,  that  is, 
to  be  more  explicit,  may  experience  conscious 
pain,  yet  the  lower  animals  and  all  plants 
only  react  mechanically  upon  stimulation, 
such  as  frictional  contact,  shock,  light,  heat, 
electricity,  etc.  To  illustrate:  when  a  dog 
howls  upon  being  hit  with  a  stone,  it  will 
generally  be  admitted  that  it  is  because  he 
suffers  pain;  but  when  an  earthworm  strug- 
gles as  the  angler  threads  it  upon  the  hook,  a 
question  arises  whether  the  movement  is  in- 
dicative of  pain  or  whether  it  is  simply  reac- 
tionarv,  like  the  quivering  of  a  mass  of  jellv 
when  struck  ;  and  when  a  twig  is  pulled  from 
a  tree  no  more  thought  of  pain  is  connected 
with  the  act  than  in  the  breaking  of  a  stone. 
In  discussing  a  subject  like  this  considerable 
difficulty  is  found  in  using  terms  in  such  a 
oi'ter^s  way  that  they  will  convey  an  exact  and  uni- 

form meaning.  In  the  task  I  have  essayed, 
nothing  is  easier  than  to  upset  the  whole  ar- 
gument   by    employing    the    words    feeling, 


Definition 


CONvSCIOUSNESS  AND   PAIN 


pleasure,  pain,  etc.,  in  some  of  their  several 
legitimate  meanings,  which  are  not,  however, 
those  suitable  for  the  topic,  and  ignoring  the 
meanings  which  alone  can  lead  to  clear  no- 
tions. To  show  the  diversity  of  usage  in  em- 
ploying the  word  "feeling"  I  will  quote  Ward 
in  the  Encyclopaedia  Britannica  (xx,  40), 
who  observes  that  "it  is  plain  that  further 
definition  is  requisite  for  a  word  that  may 
mean  (1)  a  touch,  as  /ee/j'n^  of  roughness,  (2) 
an  organic  sensation,  as  /ee/Zn^  of  hunger,  (3) 
an  emotion,  as  feeling  of  anger,  (4)  feeling 
proper,  as  pleasure  or  pain."  It  is  in  this  last 
sense  only  that  I  wish  to  employ  it.  And  it 
is  well  to  bear  in  mind  in  the  same  connec- 
tion, that  in  simple  organisms,  feeling,  like 
other  functions,  will  have  but  a  simple  and 
feeble  development,  while  in  complex  beings, 
it  will  take  on  a  diversity  commensurate  with 
the  degree  of  organic  attainment,  preserving, 
however,  throughout  the  wholegamutof  var- 
iation, the  same  fundamental  quality  of 
physical  pain  and  pleasure. 

No  less  diversity  exists  as  to  the  use  of  the 
terms  pain  and  pleasure.  In  a  recent  volume 
on  the  subject  (Marshall:  Pain,  pleasure  and 
aesthetics,  1894,  p.  169)  I  find  it  stated  that 
the  "activity  of  the  organ  of  any  content  if 
efficient  is  pleasural)le,  if  inefficient  is  pain- 
ful,"   which   is    nearly    in    accord    with    the 


philosophy  of  Lester  F.  Ward,  who  says  that 
"the  supply  of  tissue  is  attended  with  pleas- 
ure," and  "the  destruction  of  tissue  results  in 
pain"  (Monist,  v,  253).  But  both  these  ob- 
servations, it  seems  to  me,  carry  the  analysis 
too  far.  I  am  inclined  to  agree  with  Paul 
Carus,  who  says  that  although  "It  is  gener- 
ally assumed  that  pleasure  is  an  indication 
of  growth  and  pain  of  deca3%  it  has  never 
been  proven,  and  after  a  careful  consideration 
of  this  theory  I  have  come  to  the  conclusion 
that  it  is  based  upon  an  error.  Growth  is 
rarely  accompanied  with  pleasure  and  decay 
is  mostly  painless."  He  goes  on  to  remark 
that  the  most  optimistic  philosophers  look 
upon  pleasure  as  positive  and  pain  as  nega- 
tive, while  the  greatest  pessimist,  Schopen- 
hauer, turns  the  tables  and  says  pain  is  posi- 
tive and  pleasure  is  negative.  He  adds  as  his 
own  opinion  that  "an  impartial  considera- 
tion of  the  subject  will  show  that  both  pleas- 
ure and  pain  are  positive.  Pain  is  felt  when- 
ever disturbances  take  place,  pleasure  is  felt 
whenever  wants  are  satisfied"  (Monist,  i, 
559).  This  definition  accords  so  well  with 
the  usual  mode  of  thinking  and  use  of  terms 
that  I  deem  it  unnecessary  to  elaborate  it.  If 
now  it  be  admitted  that  pain  results  from  a 
more  or  less  violent  interruption  or  altera- 
tion of  the  normal  functional  state  of  the  or- 


CONSCIOUSNESS  AND   PAIN 


ganism,  we  shall  only  have  to  make  sure 
that  the  organism  knows  that  it  is  suffering 
the  pain,  and  the  basis  of  the  argument  will 
have  been  established.  It  must  be  remember- 
ed, however,  that  a  sensation  which  would  be 
called  pain,  if  of  sufficient  intensity,  when 
very  slight  might  be  called  simply  discom- 
fort. 

This  leads  us  to  a  consideration  of  what  is 
to  be  understood  by  consciousness.  It  is  in- 
advisable to  attempt  an  extended  exposition 
of  this  much  treated  and  intricate  question, 
both  for  want  of  space  and  because  meta- 
physical subjects  are  proverbially  tedious.  It 
seems  to  me  sufficient  in  order  to  make  my 
position  intelligible,  to  say  that  when  the 
organism  is  aware  of  a  feeling  of  pleasure  or 
pain,  or  of  any  other  sensation,  knowing  that 
the  same  is  located  within  its  own  organs,  it 
is  possessed  of  consciousness.  This  is  what  is 
usually  known  as  simple  sense-perception,  the 
simplest  type  of  consciousness.  In  the  higher 
and  more  complex  forms,  memory  plays  a 
constantly  increasing  part;  and  judgment, 
the  formation  of  concepts,  and  all  the  intrica- 
cies of  mental  activity  finally  enter  into  the 
problem. 

It  is  usual  to  begin  with  man,  and  say  with 
Noah  Porter  that  consciousness  is  "the 
power  by  which  the  soul  knows  its  own  acts 


LIVING  PLANTS 


and  states"  ("Human  Intellect,"  par.  67),  or 
with  Locke  that  it  is  "the  perception  of  what 
passes  in  a  man's  own  mind"  ("Human  Un- 
derstanding," H,  i.,  19),  and  then  to  pass 
down  the  scale  of  being  and  admit  the  posses- 
sion of  consciousness  in  such  animals  as  are 
thought  to  be  endowed  with  a  "soul"  or 
"mind,"  according  to  the  definition  these 
words  are  permitted  to  bear.  Anatomical 
structure  is  made  to  furnish  considerable  evi- 
dence in  this  connection.  Perhaps  Grant  Al- 
len's remarks  about  the  earwig  in  his  lucubra- 
tion on  "microscopic  brains"  present  suffi- 
cienth^  well  the  attitude  of  most  writers  at  the 
present  time.  "Of  course  most  insects  have 
no  real  brains,"  he  says.  "The  nerve  sub- 
stance in  their  heads  is  a  mere  collection  of  ill- 
arranged  ganglia  directly  connected  with 
their  organs  of  sense.  Whatever  man  maybe, 
an  earwig  at  least  is  a  conscious,  or  rather 
a  semi-conscious  automaton.  He  has  just  a 
few  knots  of  nerve-cells  in  his  little  pate,  each 
of  which  leads  straight  from  his  dim  eye,  or 
his  vague  ear,  or  his  indefinite  organs  of 
taste;  and  his  muscles  obey  the  promptings 
of  external  sensations  without  possibilit}^  of 
hesitation  or  consideration,  as  mechanicall_v 
as  the  valve  of  a  steam-engine  obeys  the  gov- 
ernor-balls" ("Evolutionist  at  Large,"  2). 
Again  in  speaking  of  slugs  and  snails  he  says: 


CONSCIOUSNESS  AND  PAIN 


"Their  nerves  are  so  rudely  distributed  in 
loose  knots  all  over  the  body,  instead  of  being 
closely  bound  into  a  single  central  system  as 
with  ourselves,  that  they  can  scarcely  possess 
a  consciousness  of  pain  at  all  analogous  to 
our  own"  (ibid,  12).  Of  course,  if  animals  of 
as  high  an  organization  as  insects  and  snails 
are  thought  to  be  meagerly  endowed  with 
sensibility,  animals  of  still  lower  grade,  and 
those  especially  that  are  without  nerves  must 
be  quite  outside  the  bounds  of  consideration, 
to  say  nothing  of  plants. 

But  there  is  another  way  in  which  to  ap- 
proach the  matter;  and  one,  it  seems  to  me, 
that  leads  to  results  more  in  accord  with  our 
present  understanding  of  the  unity  of  nature 
and  the  evolution  of  organic  forms.  Living 
protoplasm  is  a  very  unstable  substance. 
Living  organisms  of  even  the  lowest  type 
have  but  a  fighting  chance  for  continued  ex- 
istence.    Life,  asks  the  poet,  what  is  it  ? 

"A  frail  and  fickle  tenement  it  is  ; 
Which,  like  the  brittle  glass  which  measures  time. 
Is  broke  ere  half  its  sands  are  run." 

— Notes  and  Queries,  1863. 

The  smallest  and  most  structureless  being,     General 
as  well   as  the  largest  and  most  intelligent,     irritability 
must  guard  itself  against  bodilv  accidents  of 
all  kinds,  it  must  look  out  for  its  daily  means 
of  subsistence,  and  furthermore,  it  must  main- 
tain itself  against   the  encroachments  of  fel- 


74  I.IVING   I'l.ANTS 

low  beings.  The  struggle  for  existence  is  by 
no  means  a  fiction,  even  with  an  amoeba. 
What  is  the  provision,  the  device,  the  method 
by  which  the  organism  is  enabled  to  success- 
fully meet  the  destructive  and  levelling  ten- 
dencies of  the  world  outside  itself?  It  is  to  be 
found,  without  question,  in  that  general  prop- 
erty of  all  living  matter  usually  designated 
as  irritability.  If  a  bit  of  the  leaf  of  water- 
weed,  the  hair  from  a  pumpkin  stem,  an 
amoeba,  or  any  similar  vegetable  or  animal 
structures  be  placed  under  the  microscope 
and  irritated  in  some  manner,  say  by  a  light 
tap  or  shock,  sudden  change  of  temperature, 
an  interrupted  current  of  electricity,  etc.,  the 
soft  protoplasmic  portion  will  shrink  and 
change  form  in  a  characteristic  way  that 
thoroughly  justifies  us  in  saying  that  it  makes 
a  sensitive  response  to  the  stimulus.  After  a 
time  the  normal  form  and  activity  are  regain- 
ed, and  another  irritation  will  be  followed  by 
another  visible  response.  If,  however,  the  ir- 
ritation be  too  severe— if  the  tap  be  too 
strong,  the  change  of  temperature  too  great, 
or  the  electric  shock  too  intense — the  convul- 
sion which  follows  will  be  mortal,  andnofav- 
orable  environmental  conditions  or  supply  of 
energy  will  again  restore  the  life  that  has  dis- 
appeared. The  protoplasm  or  animalcule  is 
as  eenuinelv  dead  as  the  man  who  has  been 


CONSCIOl'SNESS  AND   PAIN 


knocked  over  with  a  mortal  blow.  Every  or- 
ganism, except  when  in  a  special  state  of  re- 
pose—for instance,  during  the  hibernation  of 
some  animals  and  the  period  of  a  plant's  ex- 
istence when  enclosed  in  a  seed— every  organ- 
ism of  whatever  grade  of  development  is 
possessed  of  sensitiveness  of  essentially  the 
same  character  as  that  of  the  simplest  bit  of 
protoplasm  revealed  by  the  microscope.  As 
the  organism  rises  in  the  scale  of  being, 
irritability  takes  on  a  correspondingly  varied 
development.  And  it  may  be  asserted  that 
the  recoil  when  I  accidentally  press  my  hand 
against  a  thorn  is  of  the  same  essential 
nature  as  that  of  an  amoeba  or  slime-mold 
when  pierced  with  a  sharp  point:  or  that  the 
so-called  instinct  of  the  dog  which  urges  him 
to  follow  up  the  scent  of  a  rabbit  when  hun- 
gry, has  its  basis  in  the  same  fundamental 
property  of  living  matter  as  that  which 
causes  the  lively  spores  of  the  salmon-fungus 
(Saprolegnm)  to  swim  toward  the  spot  from 
which  there  is  a  slight  emanation  of  decaying 
fish,  or  the  leaf-mildew  to  turn  and  grow 
toward  the  breathing  pore  of  a  grape  leaf,  in- 
to which  it  desires  to  enter  and  find  a  congen- 
ial place  of  development,  because  it  detects  a 
slight  escape  of  vegetable  acids  from  that  di- 
rection. 
Irritabilitv  in  its  various  forms  must,  there- 


76  LIVING   PI.ANTvS 

fore,  be  considered  the  property  of  living 
lieings  by  which  they  defend  themselves 
against  injury,  secure  food,  and  obtain  the 
best  conditions  for  existence.  But  there  is  no 
efficiency  in  irritability  unless  the  organism  is 
enabled  to  change  its  position  or  the  position 
of  some  of  its  organs  upon  stimulation,  that 
is,  it  must  be  capable  of  molar  motion.  How 
molar  motion  originated  is  a  question  into 
which  I  shall  not  enter,  although  a  most  im- 
portant one  in  a  full  exposition  of  the  subject; 
neither  shall  I  touch  upon  the  origin  of  organs 
and  some  other  related  matters  of  philosoph- 
ical importance.  It  will  suffice  in  this  con- 
nection to  point  out  that  the  preliminary 
to  every  vital  movement,  not  automatic,  is 
an  effort.  That  all  plant  and  animal  move- 
ments, not  accidental,  are  related  to  the  wel- 
fare of  the  organism  is  a  proposition  that  will 
be  generalh'  admitted ;  and  such  movements 
may  consequently  l^e  classed  as  adaptive. 
That  all  movement  having  significance  must 
at  first  have  been  adaptive  seems  to  be  suffi- 
ciently clear,  and  therefore  automatic  move- 
ments must  necessarily  have  been  derived  from 
conscious  ones.  This,  I  am  aware,  is  the  re- 
verse of  the  usual  course  of  reasoning,  and  as 
the  form  in  which  I  have  stated  it  is  too  con- 
cise to  be  readily  apprehended,  it  will  be  best 
to  give  a  few  lines  to  its  elaboration. 


CONSCIOUSNESS  AND  TAIN  77 

That  an  adaptive  movement  requires  effort, 
and  that  effort  implies  consciousness  is  the  Adaptive  move- 
first  step  in   the  argument;  that  automatic  ments  imply 
movements  must  have  been  derived  from  con-  consciousness 
scious  movements,  in  order  to  avoid   the  ab- 
surdity  that   actions  can  be  directed  toward 
an  end  by  pure  chance,  is   the  second   step  in 
the  argument.     These  steps  can  probably  be 
illustrated  by  a  concrete  example  better  than 
by  abstract  statement;   and  I   shall  take  a 
familiar  example  although  the  complexity  of 
the  conditions  give   many   opportunities   for 
being  misunderstood,   rather  than  select  an 
illustration   from   the  less    familiar    domain 
of  simple  organisms.     The  man  who  is  being 
tormented  by  a  mosquito,  that  is,  receiving  a 
stimulus  giving  rise  to  pain,  must  put  forth 
an  effort  in  order  to  move  a  hand  to  crush  the 
offender.     That  effort   must  be   a   conscious 
effort,  or  else  the  blow  would  be  aimless  and 
futile  and  stand  in  no  relation  to  the  cause. 
Butif  the  man  were  preoccupied,  he  might  aim 
a  well  directed  blow  at  the  mosquito  and  yet 
not  realize  that  any  such  thing  had  occurred. 
In  this  case  it  is  evident  enough  that  it  was 
not  the  first  time  that  he  had  performed  a 
similar  act.     The  first  time  such  a  movement 
was  made,  it  must  have  been  a  conscious  one, 
and  for  many  times  afterward,  until  it  could 
be  performed   without  conscious  effort.    All 


.IVING  PLANTS 


other  automatic  movements  maybe  similarly 
explained.  In  reference  to  the  involuntary 
movements  of  the  heart  and  other  viscera, 
Cope  has  suggested  that  they  "were  organ- 
ized in  primitive  and  simple  animals  in  suc- 
cessive states  of  consciousness,  which  stimu- 
lated voluntary  movements,  which  ultimately 
became  rhythmic"  (Organic  Evolution,  511). 
He  goes  on  to  observe  that  "the  structure  of 
the  infusoria  offers  the  structural  conditions 
for  such  a  process,"  and  proceeds  to  illustrate 
how  the  contractile  vesicle  might  have  thus 
arisen,  and  from  it  the  mammalian  heart. 
But  we  need  not  follow  him. 

Lester  F.  Ward  has  said  that  "pleasure  and 
pain  are  the  conditions  to  the  existence  of 
plastic  organisms,  pleasure  leading  to  those 
acts  which  insure  nutrition  and  reiDroduction, 
and  pain  to  those  which  will  insure  safety" 
(Psychic  Factors  of  Civilization).  Cope  has 
elaborated  theideainto  a  well  maintained  hy- 
pothesis, which  he  calls  archaesthetism.  He 
defines  it  thus:  "It  maintains  that  conscious- 
ness, as  well  as  life,  preceded  organism,  and 
has  been  the  primum  mobile  in  the  creation 
of  organic  structure.  This  conclusion  also 
flows  from  a  due  consideration  of  the  nature 
of  life.  I  think  it  possible  to  show,"  he  goes 
on  to  say,  "that  the  true  definition  of  life  is 
energy  directed  by  sensibility,  or  by  a  mechan- 


CONSCIOUSNESS  AND  PAIN  79 

ism  which  has  originated  under  the  direction 
of  sensibility''  (1.  c.  513).  With  this  view  of 
the  role  of  consciousness  the  writer  fully 
agrees. 

Let  us  now  stop  and  see  where  we  are.  I 
have  tried  to  show  that  all  organisms,  even 
to  the  very  simplest,  whether  plant  or  animal, 
from  the  very  nature  of  life  and  the  struggle 
for  its  maintenance,  must  be  endowed  with 
conscious  feeling,  pleasure  and  pain  being  its 
simplest  expression.  I  have  attempted  to 
show  that  consciousness  is  not  a  function 
superimposed  upon,  or  evolved  from  an  ad- 
vanced state  of  organic  development,  but  is 
co-extensive  with  life. 

The  hypothesis  would  likely  meet  with  con- 
siderable adherence  were  it  not  for  plants, 
which  all  writers  seem  to  think  present  an 
insurmountable  difficulty.  Paul  Carus,  the  p  ,  r  , 
learned  editor  of  the  Monist  and  author  of  in  evolution 
many  important  philosophical  treatises,  as- 
serts that  "pleasure  and  pain  are  undoubtedly 
important  factors  in  the  evolution  of  the  ani- 
mal world,  but  the  kingdom  of  plants  demon- 
strates that  theexistence  of  plastic  organisms 
with  complex  systems  of  nutrition  and  repro- 
duction and  also  devices  for  safety  is  possible 
without  pleasure  and  pain"  (Monist,  iv.  624). 
Cope  has  tried  to  get  around  the  difficulty  in 
his  work  on  the  primary  factors  of  organic 


LIVING   PLANTS 


evolution  by  assuming  that  plants  are  won- 
derfull}^  degenerate,  having  little  cause  for 
exertion,  and  behave  in  this  respect  like  para- 
sites. "We  can  understand,"  he  says,  "how 
by  parasitism  or  other  mode  of  getting  a  live- 
lihood without  exertion,  the  adoption  of  new 
and  skillful  movements  would  become  unnec- 
essary, and  consciousness  itself  would  be  sel- 
dom aroused.  Continued  repose  would  be 
followed  by  subconsciousness,  and  later  by 
unconsciousness.  Such  appears  to  be  the 
history  of  the  entire  vegetable  kingdom"  (I.e. 
509).  The  writer  believes  that  such  opinions 
as  just  quoted  are  the  outcome  of  ignorance 

^    .       .         of  the  present  status  of  botanical  science; 
Action  01  ,      '  .  1      i^   j^        1  t,        v       i        , 

plants  difficult  not  the  botany  that  teaches  about  plants— 
to  interpret  their  names,  and  the  ways  of  identifying  the 
different  kinds— but  the  botany  that  intro- 
duces the  learner  to  a  knowledge  of  their 
modes  of  living,  their  habits  and  their  physi- 
ology. Plants  are  more  difficult  to  study  and 
understand  than  animals,  because  they  are 
so  much  more  unlike  ourselves.  Vegetable 
activities  are  very  different  from  animal  ac- 
tivities; they  have  been  developed  along  dif- 
ferent lines.  It  is  only  recently  that  we  have 
begun  to  understand  them  at  all.  And  yet 
alreadv,  the  elucidation  of  plant  movements 
is  providing  a  key  to  the  study  ol  animal 
movements.    Recently  an  investigator  at  the 


CONSCIOUSNESS  AND  PAIN  81 

Zoological  Station  at  Naples  has  shown  that 
when  a  moth  flies  into  a  flame  it  is  attracted 
in  essentially  the  same  way  that  the  window 
plant  is  when  it  turns  to  the  light.  One  must 
go  to  the  tropics  to  see  the  highest  develop- 
ment of  movement  in  plants,  on  account  of 
the  high  and  uniform  temperature,  and  pos- 
sibly other  environmental  conditions.  I  have 
been  told  that  in  Java,  as  one  walks  through 
a  tangle  of  sensitive  plants,  they  will  drop 
down  in  their  deprecating  way  for  yards  un 
either  side,  as  if  suddenly  aroused  into  life 
only  to  be  again  transformed  into  lifeless 
sticks  by  some  unseen  power. 

It  is  because  plant  movements  are  so  slow, 
as  a  rule,  that  we  get  the  erroneous  idea  that 
they  are  rare.  Have  you  ever  noticed  that 
beans  and  clover  put  their  leaves  into  a  differ- 
ent position  at  night,  the  same  as  a  sensitive 
plant  does;  and  that  locusts,  lindens,  red-bud, 
and  many  other  trees  and  shrubs  do  the  same? 
Suppose  a  seed  falls  upon  the  ground  and 
germinates:  if  it  has  no  sensitiveness  by 
which  it  feels  the  action  of  gravity,  the 
chances  are  that  it  will  speedily  perish,  for 
the  root  would  not  otherwise  find  its  way  in- 
to the  soil,  except  through  accident.  There  is 
one  excellent  reason  why  plants  rarely  re- 
spond visibly  to  bodily  injury,  and  that  lies 
in  the  fact  that  they  are,  for  the  most  part. 


LIVING  PLANTS 


fixed  objects.  They  have  not  been  required  to 
learn  to  move  out  of  the  way  of  danger,  or 
to  recoil  when  hurt,  because  the  character  of 
their  structure  makes  movement  difficult, 
their  limbs  and  organs  are  not  sufficiently 
plastic,  and  their  attachment  to  the  earth  re- 
strains them,  like  Prometheus  bound. 

This  leads  me  to  say,  that  as  a  rule  we  do 
not  expect  the  right  things  of  plants ;  we  do 
not  understand  them.  Our  point  of  view  is 
not  well  chosen.  Animals  are  free  moving 
beings,  with  their  soft  parts  in  considerable 
masses,  while  plants  are  fixed  to  one  spot  all 
their  lives,  and  have  their  soft  parts  infinitely 
divided,  each  particle  being  encased  in  a 
rather  rigid  envelope.  How  can  they  act 
alike?  And  yet  both  are  organized  from  the 
same  character  of  living  matter,  which  is 
obedient  to  the  same  general  laws. 

In  another  respect  plants  differ  widely  from 
animals.  They  have  no  nervous  organiza- 
tion, and  no  co-ordinating  centers  for  deter- 
mining the  character  of  movements.  The 
movement  that  follows  a  stimulus  is  there- 
fore confined  usually  to  the  near  vicinity  of 
the  point  of  stimulation.  If  they  experience 
pain,  as  I  think  they  may,  it  can  rarely  ex- 
tend to  the  wdiole  organism,  but  the  injured 
organ  suffers  without  its  fellows  being 
affected. 


CONSCIOUSNESS  AND   PAIN  83 

Plants  as  a  class  are  not  degenerates.  In 
their  way  they  have  reached  a  high  state  of 
development,  but  it  is   not  the  development 

of  animals.    As   their  movements  are  slow,     „,    ^ 

'  Plants  not 
and  poorly  co-ordinated,  it  must  be  assumed  degenerates 
that  their  pains  and  pleasures  are  correspond- 
ingly feeble;  not  but  that  thej^  are  genuine, 
nevertheless,  and  to  them  mean  as  much  as 
ours  do  tons.  If  another  man  who  is  inferior 
to  ourselves,  if  a  horse,  a  dog,  a  bird  may  be 
made  to  suffer,  and  in  consequence  ought  to 
have  considerate  treatment,  so  may  the  sim- 
plest animals  and  so  may  all  plants. 

I  will  close  with  a  quotation  from  Grant 
Allen, and  a  comment  thereon.  "Hoeing  among 
the  flower  beds  on  my  lawn  this  morning,  for 
I  am  a  bit  of  a  gardener  inmy  way,"  he  writes, 
"I  have  had  the  ill  luck  to  maim  apoor  yellow 
slug,  who  had  hidden  himself  among  the  en- 
croaching grass  on  the  edge  of  my  little  par- 
terre of  sky-blue  lobelias.  This  unavoidable 
wounding  and  hacking  of  worms  and  insects, 
despite  all  one's  care,  is  no  small  drawback  to 
the  pleasures  of  gardening  iw  propria  persona. 
Vivisection  for  genuine  scientific  purposes  in 
responsible  hands,  one  can  understand  and 
tolerate,  even  though  lacking  the  iieart  for  it 
one's  self;  but  the  useless  and  causeless  vivi- 
section which  can  not  be  prevented  in  every 
ordinary  piece  of  farm  work,  seems  a  gratu- 


LIVING  PLANTS 


itous  blot  upon  the  face  of  beneficent  nature. 
My  only  consolation  lies  in  the  half-formed 
belief  that  feeling  among  these  lower  crea- 
tures is  indefinite  and  that  pain  appears  to 
effect  them  far  less  acutely  than  it  effects 
warm-blooded  animals."  To  which  I  have  to 
add  that  heshould  have  embraced  plants,  and 
then  concluded  that  in  proportion  to  their  de- 
gree of  organization  they  are  hurt,  and  to  the 
same  degree  deserve  consideration. 


YI. 

HOW  COLD  AFFECTS  PLANTS.* 

If  one  should  carefully  note  the  exit  of  his 
floral  acquaintances  in  the  autumn  he  would 
find  that  not  all  of  them  succumb  to  the  rigors 
of  the  cold  season  at  the  same  time.  Some 
of  the  members  of  the  plant  communities  pe- 
culiar to  meadows,  woods  and  slopes  will 
give  over  activity  at  the  first  suggestion  of 
frost,  while  others  endure  a  long  succession 
of  freezing  nights  before  they  finally  perish. 

Still  others,  the  conifers  and  evergreens,  the 
thick  bedsof  mosses,  and  the  thin  green  layers 
formed  by  the  liverworts  and  the  grayish 
coating  formed  by  the  lichens,  live  through 
arctic  winters  without  great  apparent  change, 
except  indeed  thatsomegrowand  fruit  in  and 
under  the  snow.     Between  the  groups  which 

*Given  before  the  Botanical  Seminar,   University  of  Minne- 
sota, Nov.  13th,  1897. 


LIVING  PLANTS 


are  killed  by  the  winter,  and  the  evergreens 

which  withstand  it  without  any  great  altera- 

Varying  tions  in  outward  form,   stand  the  deciduous 

reaction  trees,  which  cast  their  leaves,  and  herbaceous 

*°  ^'^  plants  with   thickened    underground    stems, 

which  withdraw  the  living  substance  from 

the  leaves   and   stems    to    the    underground 

structures,  leaving  the  entire  shoot  to  perish 

in  the  winter  storms. 

The  degree  of  cold  necessary  to  ensure  the 
death  of  any  species  depends  entirely  upon  the 
specific  constitution  of  the  protoplasm  and 
the  stage  of  development,  or  stage  of  activity 
of  the  organism  at  the  time  it  is  subjected  to 
the  low  temperature. 

According  to  numerous  tests  made  during 
the  last  half  century,  it  has  been  found  that 
many  delicately  leaved,  rapidly  growing  spe- 
cies are  killed  by  a  temperature  above  the 
freezing  point,  others  native  to  the  Arctic  zone 
are  not  injured  when  the  air  and  the  soil  in 
which  they  grow  fall  to  seventy  degrees  centi- 
grade below  the  freezing  point.  Well  matured 
and  air  dried  seeds  in  the  resting  stage  have 
been  subjected  without  injury  for  prolonged 
periods  to  the  extremest  low  temperatures 
that  can  be  produced  in  the  laboratory.  In 
one  series  of  experiments  seeds  were  immersed 
in  liquid  air  at  a  temperature  of  about  two 
hundred  degrees  centigrade  for  several  hours 


EFFECTS  OF  COLD 


with  no  resulting  damage.  From  this  last 
series  of  tests,  it  may  be  safely  said  that  the 
protoplasm  of  plants  when  in  the  proper  rest- 
ing stage  is  practically  indestructible  by  cold. 
Not  only  have  seeds  great  power  of  resistance 
to  cold,  but  they  are  capable  of  carrying  on 
growth  at  low  temperatures.  The  seeds  of 
several  -common  cereals  will  germinate  on 
blocks  of  ice  at  a  temperature  of  one  or  even 
two  degrees  below  the  freezing  point. 

If  frozen   leaves  are  taken  in  the  hand  and     Appearance 
crushed   or  bent,   they  retain  the  form  given     of  frozen 
them.      During  the  crushing,  the  breaking  of    P^^"*^ 
the  ice  can  be  heard  distinctl3^   Frozen  plants 
do  not  regain  their  elasticity  upon  thawing. 
Upon  the  contrary,  they  become  limp,  partly 
trantLparent,   and  exhibit    changes    of  color 
chiefly  due  to  the  destruction   of  the  chloro- 
phyll.     The  entire  body  of  the  plant  has  lost 
its  consistency,  and  the  different  tissues  may 
be  easily  stripped  apart.      When   exposed   to 
the  sun,  the  leaves  shrivel  and  assume  a  rusty 
brown  or  black  color.    They  entirely  resemble 
charred  leaves,  and  the  farmer  says  that  the 
frost  has  "burned  them." 

It  is  not  to  be  taken  for  granted  that  all  of 
the  cells  of  a  plant  are  equally  resistant  to 
cold.  Thus  it  is  known  that  hairs  and  the 
guard  cells  of  stomata  remainactive  when  the 


Ice  in  the 
tissues 


88  LIVING  PLANTS 

remainder  of  the  plant  is  frozen  solidly.  With- 
out doubt  other  differences  also  exist. 

To  understand  these  appearances  one  must 
recall  the  salient  features  in  the  structure  of 
the  leaf:  that  it  is  composed  of  a  mass 
of  loosely-arranged,  thin-walled,  globular, 
cylindrical  or  irregular  sacs  lined  with  pro- 
toplasm and  containing  seventy  to  ninety 
per  cent  of  their  volume  of  water.  The  loosely- 
arranged  cells  are  held  in  position  by  the 
strong  mechanical  tissue  of  the  ribs  or  nerves, 
and  the  whole  enclosed  by  the  single  layer  of 
epidermal  cells :  that  of  the  lower  side  has 
openings  (stomata)  which  permit  the  escape 
of  watery  vapor  accumulating  in  the  spaces 
among  the  inner  cells. 

If  now  a  section  is  made  of  a  frozen  leaf,  it 
will  be  found  that  the  spaces  between  the  cells 
usually  containing  air  are  filled  almost  solidly 
with  ice  crystals.  From  whence  is  this  ice  de- 
rived? It  will  be  remembered  that  the  cell 
contains  a  large  proportion  of  water,  some 
of  which  is  in  the  form  of  a  solution  of  acids, 
salts,  etc.,  in  the  cavities  of  the  cell,  and  some 
in  the  form  of  water  of  imbibition  in  the  pro- 
toplasm and  in  the  cell  wall.  The  water  of 
imbibition  may  be  imagined  as  filling  up  the 
minute  spaces  between  the  groups  of  mole- 
cules in  the  cell  wall  and  the  protoplasm .  No  vv 
it  is  a  w^ell  known   principle  in  physics  that 


EFFECTS  OF  COLU 


water  in  a  solution  and  water  in  capillary 
spaces,  or  water  of  imbibition  will  not  freeze 
until  the  temperature  falls  a  certain  amount 
below  the  freezing  point ;  and  it  will  be  perti- 
nent to  state  at  this  point  that  the  tempera- 
ture of  small  plant  bodies  is  approximately 
the  same  as  the  surrounding  air,  with  the  ex- 
ception of  the  flowers  of  certain  aroids  and 
other  plants.  Ice  then  may  not  be  formed 
until  the  temperature  of  a  plant  has  fallen 
more  or  less  below  the  freezing  point,  amount- 
ing to  two  or  even  six  degrees  below  in  some 
instances.  The  exact  point  will  vary  with  the 
specific  constitution  of  the  plant,  as  it  does 
in  solutions  of  different  substances. 

Protoplasm  even  in  its  simplest  forms  is 
highly  automatic,  and  self-regulating.  When 
the  cells  of  a  leaf  are  subjected  to  a  low  tem- 
perature, they  contract  and  a  portion  of  the  Relation  of 
water  contained  is  driven  out  into  the  inter-  the  cell  to  cold 
cellular  spaces  where  it  is  frozen.  By  this  pro- 
vision the  proportion  of  the  water  in  the  cells 
is  reduced  and  the  danger  of  ice  formation 
and  consequent  destruction  is  averted.  If 
now  the  temperature  is  again  lowered  an  ad- 
ditional amount  of  water  is  forced  into  the 
intercellular  spaces,  rendering  the  cell  solu- 
tions still  more  concentrated,  and  less  easily 
crystallized  into  ice.  This  process  may  con- 
tinue until  the  greater  part  of  the  water  has 


LIVING  PLANTS 


been  driven  out  of  the  cell  sap,  protoplasm 
and  wall,  and  may  be  seen  piled  up  in  the 
spaces  in  the  form  of  small  pillars  or  discs,  in 
many  instances  completely  filling  up  the  space 
between  the  cells  and  forcing  them  apart, 
but  not  injuring  the  protoplasm  or  the  cell 
wall  by  the  crystallization  of  water  in  their 
interstices.  It  is  thus  to  be  seen  that  the  ex- 
trusion of  water  into  the  intercellular  spaces 
is  a  protective  device  of  the  protoplasm.  In 
many  instances  the  amount  of  ice  formed  in 
the  spaces  among  the  cells  may  be  so  great  as 
to  split  the  tissues  completely  apart.  This  is 
especially  noticeable  in  trees,  and  the  sudden 
yielding  of  the  firm  wood  to  the  pressure  of 
the  ice  crystals  within  is  accompanied  by 
startling  reports  familiar  to  those  who  fre- 
quent the  forests  in  the  early  days  of  winter. 
In  manj'  of  the  herbaceous  plants  the  split- 
ting of  the  stems  is  followed  by  the  formation 
of  very  delicate  and  fantastically  arranged 
sheets  of  ice  crystals,  which  are  commonly 
known  as  "frost  flowers." 

The  excretive  power  of  protoplasm  is  not 
always  sufficient  to  enable  it  to  reduce  the 
percentage  of  water  in  the  cell  to  such  a  degree 
as  to  escape  freezing.  In  such  instances,  ice  is 
formed  inside  the  cell,  and  the  withdrawal  of 
practically  all  of  the  water  in  the  protoplasm 
to   form  the  crvstals  results   in  the  architec- 


EFFECTS  OF  COLD 


tural  disintegration  of  the  living  substance. 
It  is  as  if  all  of  the  mortar  used  in  the  con- 
struction of  a  building  had  been  irregularly 
withdrawn,  leaving  only  a  toppling,  ruinous 
pile  of  bricks. 


Fig.  8.  Spirogvra  magnified  300  times:  a,  intact;  b,  frozen 
in  ice-  the  cells  are  shrunken  but  no  ice  is  formed  in  the  cells  ; 
c,  thawed  :  the  protoplasm  is  contracted  upon  the  chlorophyll 
bands,  and  the  nucleus  is  disorganized.     Alter  Molisch 


LIVING  PLANTS 


Relation  of 
the  organism 
to  cold 


Death  above 
freezing  point 


The  formation  of  ic?  in  the  plant  does  not 
imply  its  death.  If  the  temperature  falls  to  a 
certain  point  characteristic  of  each  species  a 
disorganization  of  the  protoplasm  will  ensue, 
and  the  plant  dies  regardless  of  subsequent 
treatment.  On  the  other  hand  it  is  well 
known  that  many  plants  may  be  frozen  and 
recover  normal  appearance,  and  that  the 
death  of  others  may  be  averted  by  practices 
known  to  the  gardener.  Thus  some  frozen 
plants,  if  submerged  in  water  a  few  degrees 
above  freezing  and  allowed  to  thaw,  will  en- 
tirely recover.  If  such  plants  are  placed  in 
warm  air  to  recover,  the  ice  in  the  intercellu- 
lar spaces  gradually  melts  and  a  large  pro- 
portion of  it  evaporates  into  the  air,  while 
the  protoplasm  absorbs  only  a  small  amount. 
All  of  this  ice  was  in  the  cell  originally,  and 
its  return  is  necessary  for  the  welfare  of  the 
cell  and  the  plant.  A  frozen  plant,  thawed  in 
the  open  air,  therefore,  is  sometimes  killed  by 
loss  of  water  which  might  be  prevented  if  the 
plant  were  immersed  in  a  vessel  of  the  fluid. 
If  ice  be  actually  formed  inside  the  cells, 
however,  the  plant  dies  whether  thawed 
slowly  or  quickly,  in  dry  or  moist  media. 

The  death  of  plants  by  low  temperature 
above  freezing  point  is  due  to  related  causes. 
Acanthus,  coleus,  basils,  melons,  tobacco 
plants,  etc.,  blacken  and  die  if  exposed  to  a 


EFFECTS  OF  COLD 


temperature  of  three  or  four  degrees  above 
freezing  point  for  a  single  night.  In  such  in- 
stances the  death  of  the  leaves  is  due  to  the 
fact  that  the  chilling  of  the  roots  decreases 
their  ability  to  absorb  water  from  the  soil  as 
fast  as  itis  needed  by  the  leaves,  which  shrivel, 
blacken  and  dry  up  in  consequence.  If  one  of 
these  plants  is  placed  in  a  pot  and  the  earth 
about  the  roots  not  allowed  to  approach 
within  fourteen  degrees  of  the  freezing  point, 
the  shoot  and  leaves  may  be  exposed  to  air 
near  the  freezing  point  without  injury.  As  has 
been  shown  elsewhere  the  casting  of  autumn 
leaves  is  a  provision  of  deciduous  plants, 
whereby  the  leaves  are  cut  away  at  the  time 
when  the  absorbing  capacity  of  the  roots 
and  the  water  supply  is  decreased. 

The  power  of  excretion  of  water  from  the 
cells  by  protoplasm  is  the  primary  means  of 
protection  against  death  by  cold,  and  is  pos-  Adaptations 
sessed  by  all  plant  protoplasm.  It  is  evident,  ^2^*^  ^° 
however,  that  this  is  a  method  designed  pri- 
marily for  the  safety  of  each  individual  cell. 
The  organism  as  a  whole  may  be  expected  to 
exhibit  adaptations  to  shield  the  cells  from 
the  extremes  of  low  temperature.  The  most 
common  device  for  escaping  cold  consists  of  a 
deeply  penetrating  root  system  and  the  devel- 
opment of  underground  stems.  The  roots  are 
sent  down  to  a  depth  at  which  the  tempera- 


LIVING  PLANTS 


ture  does  not  reach  the  freezing  point,  or  does 
so  slowly,  and  rises  again  so  gradually  that 
no  harm  is  done.  The  primary  purpose  of  the 
roots  is  of  course  to  penetrate  the  soil  in  such 
manner  as  to  fix  the  plant  and  obtain  a  sup- 
ply of  mineral  salts,  and  in  so  doing  a  region 
not  subject  to  the  rigors  of  low  temperature 
is  reached.  Some  lowly-growing  plants  avail 
themselves  of  the  blanket-like  coverings  of 
leaves  and  snow  which  fall  upon  them  before 
the  extremest  rigors  of  the  winter  are  at  hand. 
Many  plants  native  in  alpine  regions  arc 
specially  adapted  to  take  advantage  of  this 
means  of  protection.  Among  them  are  some 
of  the  rhododendrons,  dwarf  junipers  and 
pines. 

The  stem  of  Pitius  hamilis  of  the  higher 
mountain  slopes,  although  eight  or  ten  inches 
in  diameter  and  strong  enough  to  stand  erect 
and  sustain  the  ample  crown,  grows  almost 
parallel  with  the  surface  and  a  few  inches 
above  it.  The  branches  which  are  ordinarily 
erect  are  very  flexible  and  easily  bent  down- 
ward, and  when  weighted  spread  themselves 
along  the  ground.  This  is  true  of  branches 
which  stand  up  to  the  height  of  a  yard  or 
more.  When  the  early  storms  set  in,  and  the 
ever  increasing  layer  of  snow  settles  down 
over  everything,  the  branches  slowly  bend 
under  the  constantly  augmented  weight,  and 


EFFECTS  OF  COLD 


finally  are  pressed  against  the  soil  unHer  many 
feet  of  snow.  In  this  position  they  are  also 
secure  from  the  shearing  action  of  moving 
masses  of  ice  and  snow  above  them.  When 
the  snow  melts  in  the  spring  the  elastic 
branches  return  to  the  upright  position,  and 
the  early  climber  may  see  the  old  leaves  plas- 
tered over  with  earth,  and  small  stones  ad- 
hering to  the  twigs  and  branches.  The  gar- 
dener imitates  the  action  of  these  pines  when 
he  bends  rose  bushes  and  small  shrubs  to  the 
ground  and  covers  them  with  earth  and  straw. 

A  very  interesting  method  of  avoiding 
death  by  cold  is  afforded  by  many  aquatic 
plants.  Species  which  float  on  the  surface  of 
water  owe  their  buoyancy  to  small  bubbles 
of  gas  in  or  between  the  cells.  On  the  ap- 
proach of  winter,  the  gas  is  given  off,  and  the 
plant  sinks  to  the  bottom,  either  in  the  form 
of  spores  or  the  entire  vegetative  body  of  the 
plant. 

In  such  forms  as  the  water  lily,  the  leaves 
and  flowers  die  down  and  the  main  stem  of 
the  plant,  a  bulky  rhizome  loaded  with  food, 
is  securely  imbedded  in  the  mud  below  the 
freezing  line.  At  the  beginning  of  each  season 
new  leaves  and  flower-stalks  are  sent  to  the 
surface. 

Perhaps  the  most  interesting  adaptation  is 
that  offered  by  such   aquatic  plants  as  the 


LIVING   PLANTS 


pondweeds,  bladderworts  and  stoneworts 
which  root  in  the  mud  at  a  few  feet  below  the 
surface.  With  the  approach  of  autumn  the 
tips  of  the  stems  grow  in  the  form  of  a  thick 
shoot  with  short,  crowded  leaves  which  are 
termed  hihernacula.  The  hibernacula  finall\' 
break  loose  from  the  stem,  which  dies,  and 
sink  to  the  bottom  before  ice  formation  sets 


%^ 


c. 


Fig.  9. — a.  Hibernaculwni  ot  Utricnlaria  in  October,  b.  Ter- 
minal portion  of  stem  in  swmmer.  c.  Hibernacnlum  of  Philo- 
tria  Canadensis  (Elodea  Canadensis),  d.  Terminal  portion  of 
stem  in  summer:     photographed  in  the  air. 

in,  and  lie  quiescent  during  the  winter.  After 
the  spring  thaws,  if  one  rows  over  the  shal- 
lows near  a  lake  shore,  he  may  see  the  hiber- 
nacula resting  on  the  bottom,  and  as  soon  as 
the  sun's  rays  have  warmed  the  water  suf- 
ficiently to  allow  growth,  a  few  rise  to  the 
surface,  and  all  begin  to  send  out  roots  from 
the  lower  end,  and  stems  form  at  the  upper 


EFFECTS  OF  COLD 


end,  with  the  result  that  the  entire  plant  is 
reproduced  within  a  short  period.  Some 
species  form  a  hibernaculum  at  the  tip  of  each 
branch,  with  the  result  of  multiplying  the 
plant  by  this  method. 

Some  plants  as  a  whole  avoid  low  temper- 
atures by  growing  in  such  a  manner  as  to  be 
covered  with  a  protecting  blanket  of  leaves 
and  snow  ;  and  others  retire  to  a  depth  below 
the  frost  line  in  the  medium  in  which  the)^  live. 
Winter  buds  are  of  course  devices  for  the 
protection  of  growing  tips  against  sudden 
changes  of  temperature  and  moisture,  as  well 
as  from  mechanical  injuries  due  to  wind,  sleet, 
snow  or  ice. 

As  a  conclusion  to  be  derived  from  the  fore- 
going paragraphs  it  is  to  be  seen  that  proto- 
plasm seeks  to  avoid  danger  of  disorganiza- 
tion from  the  formation  of  ice  in  its  interstices 
by  getting  rid  of  a  portion  of  its  water  when 
the  temperature  falls,  and  the  death  of  a  plant 
does  not  necessarily  follow  "freezing."  Death 
by  cold  may  be  due  to  the  direct  action  of 
cold,  or  to  the  consequent  desiccation  of 
the  tissues.  When  due  to  the  latter  cause  it 
may  be  brought  about  by  temperatures  above 
the  freezing  point. 

That  temperature  has  been  a  most  impor- 
tant factor  in  the  evolution  of  the  vegetable 
kingdom,  as  well  as  in  the  distribution  of  the 


LIVING  PLANTS 


separate  forms,  is  evident  when  one  considers 
the  vegetation  of  a  mountain  from  its  base 
with  its  warm  breezes  and  soft  sunshine  to 
the  bleak  summit  with  icy  winds,  cold  nights 
and  ravines  filled  with  snow. 


TWO  OPPOvSING  FACTORS  OF  INCREASE.* 

The  energies  of  the  plant  are  used  for  two 
general  purposes:  the  development  and  main- 
tenance of  the  vegetative  parts,  and  the  for- 
mation of  special  reproductive  bodies.  In 
some  respects  the  efforts  of  the  plant  in  these 
two  directions  are  antagonistic.  Thevegeta-  Two  sides 
five  part  consists  of  root,  stem,  foliage,  etc.,  *°  P'^'^*^ 
and  at  first,  and  sometimes  for  a  long  period 
in  the  life  of  the  individual,  the  energies  of  the 
plant  are  wholly  absorbed  in  increasing  the 
size  and  promoting  the  functional  activities  of 

*Condensed  from  two  articles:  one  in  collaboration  with 
Miss  K.-itherine  E.  Golden,  entitled  "Weight  of  the  Seed  in  Re- 
lation to  Pi-oduction,"  published  in  Agricultural  Science,  May. 
1891;  and  another  entitled  "A  New  Factor  in  the  Improve- 
ment of  Crops  ,"  read  before  the  Society  for  the  Promotion  of 
Agricultural  Science,  August,  1893,  and  published  in  its  Pro- 
ceedings and  in  Agricultural  Science,  September,  1893. 


LIVING  PLANTS 


these- organs,  all  being  connected  with  the 
welfare  of  the  individual  plant.  After  a  time 
special  reproductive  structures  are  developed, 
consisting  of  seeds  or  spores  and  the  accom- 
panying parts  that  aid  in  their  protection  and 
dissemination.  They  find  their  use  in  continu- 
ing the  race,  that  is,  in  providing  for  another 
generation  of  individuals. 

The  formation  of  the  vegetative  part  and 
the  formation  of  the  fruiting  part  may  be 
treated  as  separate  tendencies  in  plant  life. 
They  rarely  proceed  pari  passu,  for  usually  if 
one  is  favored,  the  other  is  less  favored.  This 
is  popularly  expressed  by  saying  that  the 
plant  runs  to  leaves,  or  runs  to  vine,  or  on 
the  other  hand  that  it  runs  to  seed,  or  it  over- 
bears. 

The  portion  of  the  plant  having  economic 
value  for  food  belongs  sometimes  to  the  vege- 
tative, sometimes  to  the  reproductive  side. 
Most  fodders,  and  many  culinary  vegetables, 
such  as  cabbage,  radish,  lettuce  and  aspara- 
gus, belong  to  the  vegetative  part,  while  the 
grains,  fruits  and  such  vegetables  as  peas, 
beans,  tomatoes  and  egfs;  plant,  belong  to  the 
reproductive  side.  The  object  of  cultivation 
is  to  increase  the  size  and  quality  of  the  part 
used,  and  it  is  evident,  therefore,  that  one  re- 
quirement of  the  husbandman  must  be  to 
learn  the  conditions  which  promote  the  de- 


FACTORS  OF  INCREASE 


velopment  of  the  particular  side  of  the  plant 
to  which  the  crop  in  question  belongs. 

But  it  is  not  from  the  standpoint  of  the  cul- 
tivator that  the  present  article  was  written, 
but  rather  from  that  of  the  evolutionist,  al- 
though the  illustrations  being  drawn  from 
cultivated  plants  make  it  easy  to  see  prac- 
tical applications  of  the  conclusions. 

It  has  been  pointed  out  that  among  the 
lower  animals,  a  sudden  check  to  growth  in- 
creases reproduction.  I  wish  to  expand  that  Nutrition  and 
statement  into  the  much  broader  and  more  development 
wideW  applicable  generalization  that  a  de- 
creasein  nutrition  during  the  period  of  growth 
of  an  organism  favors  the  development  of  the 
reproductive  parts  while  abridging  the  vege- 
tative parts.  The  converse,  that  an  increase 
in  nutrition  favors  the  vegetative  parts  while 
abridging  the  reproductive  parts,  is  equally 
true. 

Unimpeachable  statistics  are  not  abundant, 
for  experiments  l3earing  directly  upon  the 
problem  have  not  been  undertaken,  and  ser- 
viceable data  culled  from  the  supplementary 
records  of  other  experiments  are  not  very 
complete  or  numerous.  Enough  are  obtain- 
able, however,  to  lend  very  material  aid  to- 
ward estal)lishing  the  generalization. 

The  cultivator  employs  no  method  so  fre- 
quently for  enhancing  the  value  of  his  harvest 


LIVING  PLANTS 


as  increasing  the  fertility  of  the  soil.  It  is  a 
method  of  giving  the  plants  a  greater  supply 
of  nutriment,  whereby  they  grow  larger  and 
yield  more.  If  the  principle  just  stated  holds 
true,  however,  the  increase  will  be  greater 
proportionally  for  the  stems,  leaves  and  roots 
than  for  the  seeds  and  fruits.  The  data  pro- 
vided b3^  Latta  from  experiments  conducted 
in  Indiana  bear  this  out.  Wheat  grown 
u])on  fertilized  and  unfertilized  areas,  averag- 
ing the  results  of  three  seasons,  1889-91, 
showed  a  decided  gain  in  both  straw  and 
grain  due  to  the  richer  soil ;  but  upon  exam- 
ining into  the  relative  increase  of  straw  and 
grain,  it  is  very  evident  that  while  the  increase 
in  yield  of  grain  was  considerable,  it  was  by 
no  means  so  great  as  the  increase  of  straw, 
and  that  the  proportion  of  straw  to  grain 
was,  in  spite  of  the  increased  yield,  in  reality 
lessened.  (See  table  i.,  page  116.)  Essentially 
the  same  results  are  evident  in  data  obtained 
by  Caldwell  in  Pennsylvania  with  corn,  aver- 
aging the  results  of  ten  years,  1881-90, 
(omitting  1887,  the  crop  being  destroyed  by 
insects).     (See  table  ii.) 

A  very  different  method  of  increasing  yield 
is  the  treatment  of  seed  grain  before  sowing 
to  a  short  bath  in  hot  water.  It  is  especially 
interesting  to  find  that  this  method  develops 
the  same  reciprocal    relations    between    the 


FACTORS  OF  INCREASE 


vegetative  and  reproductive  parts  of  the  har- 
vest as  in  the  preceding  cases.  In  a  crop  of 
wheat  (see  table  iii)  thus  treated  it  was 
found,  that  while  the  total  weight  of  straw 
and  grain  was  both  as  a  whole  and  separately 
increased  by  the  hot  water  treatment,  the 
yield  of  grain  was  lessened  as  compared  with 
the  yield  of  straw. 

If  we  turn  from  the  statistical  method  of 
demonstration  and  appeal  to  general  obser- 
vation, an  overwhelming  array  of  facts  can 
be  brought  to  bear. 

It  is  a  common  observation  that  plants  in 
too  rich  soil  run  to  leaves  instead  of  fruit. 
Every  farmer  knows  that  he  can  expect  little 
or  no  grain  from  an  excessively  rich  spot  of 
ground,  although  the  plants  grow  far  taller 
and  larger.  The  orchardist  root-prunes  his 
trees  to  bring  them  into  bearing,  when  they 
prove  to  be  unusually  backward;  the  florist 
permits  his  plants  to  become  pot  bound  to  in- 
duce them  to  flower  more  freely;  certain 
slow  acting  diseases,  e.  g.,  peach  yellow,  and 
cotton  rust,  increase  and  hasten  the  fruiting. 
A  wide  range  of  such  general  facts  could  be 
cited,  familiar  to  every  one  having  experience 
in  such  lines.  In  this  connection  Professor 
Atkinson,  of  Cornell  University,  has  called 
attention  to  the  longer  time  that  elapses  be- 
fore spores  are  formed  when  certain  bacteria 


:.IVING  PLANTS 


are  provided  with  more  abundant  food  mater- 
ial. A  customary  culture  gave  a  crop  of 
spores  in  15-20  hours,  a  culture  with  fewer 
germs  (second  dilution)  in  36  hours,  and  one 
with  still  fewer  germs  (third  dilution)  in  48— 
72  hours. 

The  prolificacy  of  weeds  in  sterile  soil  is  a 
matter  of  common  observation.  The  great 
ragw^eed  in  poor  soil  produces  a  crop  of  seeds 
when  but  a  few  inches  high,  and  the  same  is 
true  of  other  weeds,  especially  noticeable  in 
normally  tall  ones.  Wild  plants  rooted  in 
thin  soil  on  rocks  often  bear  single  flowers  as 
large  as  all  the  remainder  of  the  plant.  Anal- 
ogous development  may  be  seen  in  some  alpine 
plants. 

As  a  summary  of  the  evidence  already 
brought  forward  it  is  plain  that  the  environ- 
mental conditions  of  plant  existence  have  a 
disproportionate  effect  upon  the  two  sides  of 
plant  life,  the  vegetative  and  the  reproductive. 
An  increase  in  available  supply  of  food,  as 
when  the  farmer  fertilizes  his  fields,  an  earlier 
and  stronger  start  in  spring  as  in  the  case  of 
wheat  treated  to  a  bath  in  hot  water  before 
sowing,  the  larger  amount  of  food  as  when 
fewer  and  fewer  bacteria  are  placed  in  same 
amount  of  culture  media,  all  show  a  favoring 
action  upon  the  vegetative  part  greater  than 
obtains  with  the  reproductive  part.     On  the 


FACTORS  OF  INCREASE 


Provision  for 


other  hand,  checking  growth  by  root  pruning 
or  by  keeping  plants  in  undersized  pots,  re- 
ducing the  general  vitality  by  slow  disease, 
and  depriving  the  plant  of  sufficient  soil  and 
moisture,  show  a  favoring  action  upon  the 
reproductive  part  in  hastening  and  multiph^- 
ing  the  formation  of  flower  and  seed  far  in 
excess  of  the  development  attained  by  the 
vegetative  part. 

As  a  factor  to  insure  perpetuity  this  law  is 
evidently  important  in  guarding  against  ex- 
termination, for  the  poorer  the  conditions  for  perpetuity 
growth,  the  more  effort  the  organism  puts 
forth  toward  seed-bearing.  One  cannot  fail 
to  be  impressed  by  the  thought,  however, 
that  if  this  be  a  general  law  of  nature,  it 
would  seem  to  imply  that  the  weakest  and 
least  favored  individuals,  being  most  fruitful, 
are  most  likely  to  be  perpetuated,  which  is  in 
evident  contradiction  to  the  accepted  theory 
of  natural  selection  and  to  common  observa- 
tion. 

There  is,  however,  another  factor  which 
comes  into  play  here,  as  a  corrective  of  this 
tendency  to  deterioration  of  the  race,  and  it 
is  to  this  law  that  special  attention  will  now 
be  directed . 

In  all  the  methods  of  increase  in  rate  of 
growth,  so  far  brought  forward,  the  change 
has  been  due  in  the  main  to  external  agencies. 


LIVING   PLANTS 


and  the  increased  growth  was  found  to  be 
correlated  with  decrease  in  amount  of  repro- 
duction. Th-^re  are,  however,  methods  of  in- 
crease in  rate  of  growth,  arising  from  causes 
inherent  within  the  organism,  that  tend  in 
quite  a  different  direction,  in  fact,  are  opposed 
Size  to  those  already  cited.    The  best  illustration, 

of  seeds  ^^^  ^j^g  q^I^  q^^  ^q  \jq  given  in  this  article,  is 
that  shown  by  the  size  of  seeds.  It  may  be 
stated  as  a  general  law  that  large  seeds  pro- 
duce stronger  plants  with  a  greater  capacity 
for  reproduction  than  small  seeds  of  the  same 
kind. 

That  larger  seeds  produce  stronger  plants, 
that  is,  plants  possessing  both  heavier  veg- 
etative parts  and  larger  yield  of  fruit,  can  be 
shown  by  abundant  experimental  data. 

To  be  sure  there  is  quite  a  common  belief 
that  the  size  of  the  seed  has  no  material  effect 
upon  the  product;  that,  provided  a  due  re- 
gard be  paid  to  vitality,  any  size  of  seed  will 
answer  the  purpose  of  propagation.  This  be- 
lief is  one  of  long  standing,  and  is  also  held 
by  some  men  of  eminence.  Sir  Joseph  Banks, 
one  of  the  leaders  in  agriculture  of  a  hundred 
years  ago,  advocated  the  use  of  small  seed  as 
answering  the  purpose  of  the  farmer  "as  effect- 
ually as  the  largest."  He  had  wheat  especial- 
ly in  mind,  and  as  the  largest  grains  contain 
the  most  flour,  the  use  of  the  large  instead  of 


FACTORS  OF  INCREASE 


the  small  seed  for  sowing  seemed  to  him  "un- 
necessary waste  of  human  subsistence."  In 
recent  years  the  distinguished  scientist,  Hab- 
erlandt,  has  given  expression  to  essentially 
the  same  opinion.  He  beheves  it  is  chiefly  the 
strain  and  the  favorable  conditions  for  growth 
that  influence  the  product,  and  not  the  weight 
of  the  seed.  He  doubtless  represents  the  opin- 
ions of  a  large  percentage  of  cultivators  of  the 
present  time,  inclusive  of  many  good  thinkers. 
Probably  a  fair  statement  of  the  general  opin- 
ion would  be  that  if  a  strain  is  to  be  kept  up  to 
its  full  vigor,  or  if  improvement  is  desired, 
careful  selection  of  the  largest  seed  is  indis- 
pensable, but  that  the  difference  between  the 
use  of  the  large  and  small  seed  will  not  be  no- 
ticeable in  the  first  year's  crop.  This  view  is 
not,  however,  borne  out  by  experiment,  as 
we  will  see. 

The  amount  and  strength  of  the  early 
growth  from  the  seed  has  been  studied  by 
Marek,  who  experimented  with  beans  and 
peas.  The  seeds  were  laid  between  moist 
blotting  paper  for  seventeen  days,  and  then  Early  growth 
measurements  were  taken  of  the  length  and 
diameter  of  the  primary  and  lateral  roots  and 
of  the  stem.  The  figures  all  stood  higher  for 
the  large  seeds  than  for  the  small  seeds,  except 
for  the  length  of  the  pea  stem.  Similar  ex- 
periments were  carried  out  by  von  Tautphous, 


LIVING   PI-ANTvS 


who  used  from  two  to  four  sizes  each  of  wheat, 
barley,  rye,  oats,  corn,  beans  and  peas.  He 
measured  the  lengths  of  the  plumule  and 
radicle  from  day  to  day  for  two  weeks.  His 
conclusion  was  that  the  larger  and 
heavier  the  seed,  the  stronger  the  develop- 
ment. He  found,  however,  an  apparent 
exception  in  peas,  as  did  Marek,  in  which  the 
main  root  and  stem  are  shorter  the  larger  the 
seed.  But  in  this  case  it  was  noted  that  the 
extra  strength  is  expended  in  lateral  growth, 
forming  a  thicker  stem  and  more  side  rootlets, 
thus  bringing  the  apparent  anomaly  into  line. 
A  subsequent  experiment  by  Marek  was  car- 
ried somewhat  further.  Three  sizes  of  English 
beans  w^ere  planted  April  24th,  and  their 
growth  noted  up  to  maturity,  July  12th,  with 
the  result  that  the  larger  the  seed  the  taller 
the  stems  and  the  more  numerous  and  larger 
the  leaves.  It  also  occurred  to  him  to  test  the 
force  exerted  by  roots  of  seedlings  in  piercing 
the  soil,  and  in  this  respect  also  the  off- 
spring of  large  seed  showed  marked  superior- 
ity over  those  from  small  seed. 

Taking  into  account  now  the  harvest,  we 
find  some  excellent  experiments  with  clear  re- 
Final  yield  suits.  Trial  of  large  and  small  seed  roughly 
separated  by  sifting  was  made  by  Gofif  with 
onion,  cauliflower,  turnip  and  cabbage,  with 
some  gain  in  favor  of  the  large  seed  in  all  but 


FACTORS  OF  INCREASE 


the  last,  and  also  made  by  Latta  with  wheat, 
who  also  obtained  gain  for  the  large  seed. 

Lehmann  separated  peas  into  three  grades, 
large,  medium  and  small,  and  planted  528 
seeds  of  each.  The  germination  showed  that 
the  larger  seeds  were  possessed  of  greater  in- 
herent strength  than  the  smaller,  the  number 
of  seeds  growing  from  each  lot  being 480, 478 
and  423 respectively.  The  yield  in  peas,  pods 
and  vines,  taken  separately  or  together,  and 
estimated  per  plant  or  as  total  weight,  gave 
the  largest  figures  for  the  product  of  the  largest 
seed,  and  intermediate  figures  for  the  product 
of  the  medium  seed.     (See  tables  iv  and  viii.) 

An  experiment  in  this  line  with  corn  was 
conducted  by  the  writer  in  1889.  Thirty  ker- 
nels from  a  single  ear  of  white  dent  corn  were 
separately  weighed  of  which  six  grew  that 
were  over  400  miUigrams  each,  and  nine  that 
were  under  300  milligrams  each.  The  pro- 
duct of  these  fifteen  plants  gave  a  greater 
average  weight  of  ears  for  the  large  than  for 
the  small  seed,  which  was  also  true  of  the 
cobs  and  kernels  taken  separately.  (See 
table  v). 

The  accompanying  graphic  illustration  of 
these  results  brings  out  the  differences  in  the 
weight  of  the  kernels  even  more  strikingly. 
The  solid  line  indicates  the  product  from  large 
seed  and  the  interrupted  line  from  small  seed. 


LIVING   PLANTS 


The  diagram  as  a  whole  shows  the  variation 
at  different  parts  of  the  ear,  the  butt  being  to 
the  left  and  the  tip  to  the  right. 

Thus  far  we  have  given  the  results  of  ex- 
periments in  all  of  which  the  seed  was  pro- 
vided the  same  ground  space  without  regard 


18 
17 
16 

J 

\ 

/ 

\ 

/ 

' ■ 

N 

1 

\ 

/ 

'^ 

-- 

N 

^ 

\ 

1 

~ 

-- 

\ 

12 
11 
10 

'/ 

\ 

- 

-r. 

on, 

la, 

j-e 

see 

t^s 

\^ 

^^_^ 

-— 

^ 

- 

-I 

on. 

sm 

«N 

see 

is 

\ 

/ 

^ 

5      6      7     8 


10  11    12   13   14    15    16 


Fig.  10. — Illustratiug  the  product  from  larere  and  small  seeds 
of  com.  Data  for  the  curves  were  obtained  by  weighing  the 
kernels  on  each  ear  of  the  product  by  fifties  from  base  to  tip. 
The  heaviest  lot  of  fifty  came  not  far  from  the  base.  These 
maxima  were  averaged  and  marked  "M,"  and  the  next  fifties 
right  and  left  in  succession  were  averaged  in  the  same  way. 
Figures  along  the  bottom  of  the  diagram  show  position  of 
each  fifty  seeds,  and  along  the  side  the  average  weight  in 
grams.  The  position  of  the  ear  of  corn  above  corresponds  to 
the  curves. 

to  size,  and  the  data  show  that  the  large  seeds 
give  larger  returns  than  the  small  seeds.  It 
would  be  natural  to  suppose  that  if  the  small 


FACTORS  OF  INCREASE 


seeds  were  placed  correspondingly  closer  to- 
gether, or  in  other  words,  if  the  seeds  were 
planted  according  to  weight  instead  of  num- 
ber, the  results  might  be  reversed.  For  it  is 
evident  that  the  same  weight  or  measure  of 
seed  will  contain  a  much  larger  number  in 
case  of  small  seeds  than  of  large,  and  in  plant- 
ing the  small  seeds  will  require  less  ground 
area  for  development,  and  consequently  a 
greater  number  of  plants  can  mature  upon  an 
equal  space. 

This  phase  of  the  question  has  been  tested 
by  Lehmann.  He  planted  188  grams  each  of 
large,  medium  and  small  peas  upon  equal 
sized  plats  of  ground,  and  although  there 
were  more  than  twice  as  many  small  seeds  as 
large,  and  nearly  once  and  a  half  as  many 
medium  seeds  as  large,  still  the  harvest  was 
greatly  in  favor  of  the  larger  seeds,  both  per 
area  and  per  plant.      (Data  in  table  yl,  page 

118). 

A  practical  lesson  is  very  pointedly  brought 
out  here,  that  in  sowing  farm  seeds  the 
amount  of  the  harvest  depends  quite  as  much, 
and  it  may  be  more,  upon  the  quality  (size) 
of  the  individual  seeds  as  upon  the  w^eight  or 
measure  sown  per  acre. 

Is  it  not  apparent  that  large  seeds  show     Superiority  of 
great  superiority  over  small  seeds  in  numer-    large  seeds 
ous  requirements   that  enter  into   successful 


LIVING  PLANTS 


plant  life  ?  In  the  first  place,  a  larger  propor- 
tion germinate,  and  this  evidence  of  the  pos- 
session of  greater  strength  is  followed  up  by 
more  vigorous  growth  and  the  display  of  in- 
creased capacity  for  overcoming  obstacles. 

The  resulting  plants  attain  to  greater  de- 
velopment, as  the  size  of  leaf,  length  of  stem 
and  weight  of  any  part  or  of  the  whole  plant 
abundantly  proves.  It  is  especially  noticeable 
that  in  this  displa}^  of  greater  vigor  both 
vegetative  and  reproductive  parts  are  benefit- 
ted ;  and  while  the  individual  plants  are 
making  a  more  successful  fight  in  jDromoting 
their  present  welfare,  they  are  enabled  to  pro- 
vide more  abundantly  for  the  next  generation, 
bj'  producing  a  l^etter  crop  of  seeds. 

Although  the  proposition  in  relation  to  size 
of  seed,  with  which  we  started,  has  been  illus- 
trated and  established  so  far  as  present  space 
permits,  yet  in  order  to  compare  more  fully 
the  tendency  of  the  powers  of  the  plant  derived 
from  the  two  sources,  which  for  convenience 
we  may  call  acquired  and  hereditary,  the  for- 
mer coming  from  food,  light,  warmth,  and 
other  external  conditions,  and  the  latter  from 
the  energy  stored  in  the  seed,  it  is  necessary 
to  bring  forward  still  other  data.  We  may 
venture  to  formulate  this  proposed  extension 
of  the  law  relating  to  the  size  of  seed  thus:  large 
seeds  give  rise  to  plnnts  with  a  greater  deve- 


FACTORvS  OF  INCREASE 


lopment  of  the  reproductive  parts,  and  less 
of  vegetative  parts,  than  small  seeds  do. 

It  is  intended  here  to  directly  compare  the 
reciprocal  relations  of  the  two  sides  of  the 
plant  as  influenced  by  the  parent  seeds.  The 
data  may  be  taken  by  weighing  the  fruiting 
portion  and  comparing  it  with  the  weight  of 
all  the  remainder  of  the  plant,  both  done 
when  at  their  best  development;  or  other 
methods  may  be  used. 

Excellent  data  are  supplied  from  the  re- 
searches of  Lehmann  (see  table  viii).  He 
grew  large,  medium  and  small  peas,  over  400 
of  each  lot,  and  obtained  plants  that  were 
heavier  for  the  larger  seed  in  both  their  vege- 
tative and  their  reproductive  parts,  /.  e.,  the 
leaves  and  stalks  for  the  vegetative  part  and 
the  peas  and  pods  for  the  reproductive  part. 
And  yet  when  the  weight  of  the  vegetative 
portion  is  compared  with  that  of  the  repro- 
ductive portion  of  each  lot,  it  is  clear  that  the 
fruiting  part  has  attained  a  stronger  devel- 
opment in  comparison  to  the  remainder  of 
the  plant  in  the  lots  from  larger  seeds.  To 
state  the  facts  in  another  way,  the  larger 
seeds  not  only  grow  larger  plants,  but  those 
which  have  fruiting  parts  more  strongly  de- 
veloped than  the  associated  vegetative  parts. 

Interesting  data  are  furnished  by  Birnerand 
Troschke  using  oats  and  peas,  and  by  Marek 


Vegetative  and 
fruiting  parts 
compared 


114  LIVING   PLANTS 

with  peas.  The  last  investigator  found  that 
the  weight  of  peas  of  first  quality  was  nearly 
three-fourths  of  the  whole  harvest  raised  from 
large  seeds,  and  only  about  one-third  of  that 
from  small  seeds.  (See  table  vii.)  In  this 
case,  therefore,  the  large  seeds  not  only  gave 
a  much  better  total  yield,  but  far  more  seed 
material  of  high  grade  with  which  to  con- 
tinue the  strain. 

Marek,  in  Germany,  experimenting  with 
wheat  (see  table  ix),  and  Plumb,  in  the  Uni- 
ted States,  with  oats  (see  table  x),  have 
demonstrated  the  same  fact.  Both  have  pro- 
vided data  which  show  that  the  amount  of 
grain  in  comparison  with  the  straw  was 
greater  in  case  of  large  seeds  than  of  small 
ones. 

Statistical  evidence  of  this  kind  might  be 
greatly  extended,  although  observations  have 
rarely,  if  ever,  been  instituted  with  this  par- 
ticular end  in  view.  Casual  observations 
give  no  aid  to  this  part  of  the  inquiry,  as  the 
differences  are  obscured  by  other  factors  which 
stand  out  more  prominently.  What  the  eye 
cannot  detect,  however,  is  readily  and  unmis- 
takably revealed  by  the  rule  and  balance. 

So  far  as  data  can  be  marshalled  at  present, 
there'appears  good  reason  to  believe  that 
large  seeds,  besides  giving  rise  to  larger  and 
more  fruitful  plants,  also  possess  an  inherent 


KACTOKS  OF  INCREASE 


tendency  to  accentuate  the  reproductive  side 
of  the  resulting  development.  If  peas  are 
sown,  the  largest  seeds  not  only  give  rise  to 
the  largest  plants,  with  the  greatest  weight 
of  pods  and  of  seeds,  but  to  an  excess  of 
fruitage  when  compared  with  the  remainder 
of  the  plant ;  and  in  a  similar  way  with  other 
kinds  of  plants,  the  largest  parent  seeds  give 
the  greatest  returns  of  fruit  and  daughter 
seeds,  both  absolutely  and  also  in  comparison 
with  the  growth  of  leaf,  stem  and  root.  It  is 
to  be  understood,  of  course,  that  we  are  not 
attempting  to  deal  with  single  plants,  but 
with  sufficiently  large  numbers  to  neutralize 
individuality  and  small  accidents,  which  some- 
times produce  most  unaccountable  variations. 

If  we  consider  the  bearing  of  all  the  data  External  and 
now  brought  forward,  it  seems  reasonable  internal  factors 
to  ass-ume  that  in  the  ultimate  analysis  we 
are  dealing  with  acquired  and  inherited  tend- 
encies. In  the  one  case  the  impulse  or  stim- 
ulus to  development  comes  from  without ;  it 
is  environmental,  and  acts  more  strongly  up- 
on the  somatogenic  portion  of  the  plant, 
while  in  the  other  case  it  is  inherent  in  the  or- 
gani.iation  of  the  seed  and  derived  from  the 
parent  plant.  Whatever  the  explanation  of 
the  origin  may  be,  however,  it  seems  certain 
that  these  two  opposing  factors  of  increase 
play  an  important  role  in   the  economy  of 


LIVING  PLANTS 


nature.  As  the  food  supply  is  lessened,  a 
greater  effort  is  made  on  the  part  of  the 
parent  plant  to  enhance  the  chances  for 
perpetuity;  but  at  the  same  time  the  largest 
seeds,  having  the  greatest  potentiality,  stand 
the  best  chance  in  the  future  struggle;  and 
although  the  best  nourished  plants  produce 
the  fewest  seeds,  their  greater  size  gives  them 
decided  advantages  over  seeds  from  starved 
plants.  The  two  laws  acting  together,  there- 
fore, aid  in  maintaining  the  perpetuity  of  the 
species  and  its  full  measure  of  vigor. 


I.     Yield  of  Wheat  on  Fertilized  and  Unfertilized 
Ground. 


(Weights  calculated  to  the  acre.) 


Treatment. 

Weight  of 
straw  in 
pounds. 

Weight  of 
grain  in 
pounds. 

Proportion 
of  straw 
to  grain. 

Unfertilized 

2813 
4279 
3971 
2727 
3699 
3361 
2894 

1602 
1938 
1884 
1506 
1818 
1728 
1512 

1-0  56 

Commercial  Fertilizer....! 

1:0.45 
1:0.47 

Stable  manure ! 

1:0.49 
1:0.51 

Average  unfertilized 

2811 
3880 

1540 

1.842 

1:0.55 
1:0.48 

FACTORS  OF  INCREASE 


II.    Yield  of  Corn  and  Wheat  o.\  Fertilized  and 
Unfertilized  Ground. 

(Weights  calculated  to  the  acre.) 


Treatment. 


(Unfertilized.. 
^Fertilized 


„^^,^  /Unfertilized, 

'-^^"^  \Feitilized.... 


Weight  of 
stalks  in 
pounds. 


Weight  of 
grain  in 
pounds. 


958 
1246 


Proportion 

of  stalks  to 

grain. 


III.    Yield  of  Wheat  with  and  without  Hot  Water 
Treatment. 


(Weights  calculated  to  the  acre.) 


Treatment. 

Weight 
of  straw. 

Weight 
of  grain. 

Proportion 
of  straw 
to  grain. 

Untreated                     

3737 
4555 

1716 
1908 

1:0.46 

Hot  water  bith 

1:0.42 

LIVING  PI-ANTS 


IV.  Product  from  Large  and  Small  Peas. 


Size. 

0  ^ 

n  3 

c 

0 
3  ?* 

Z 

0 

0 
3 

Wt. 

of  harvest  in  grams. 

Peas. 

Pods. 

Vine. 

Total. 

Large 

Medium  .. 
Small 

273 
221 
160 

528 
528 
528 

480 
478 
423 

1814 

1495 

998 

437 
357 

280 

3170 
2630 
2010 

5421 
4482 
328S 

V.  Yield  of  Indian  Corn  from  Large  and  S.mall  Seed. 


Size. 

Ay.  Wt.  of 

kernels 

in  milligrams. 

Av.  Wt.  of 

cobs 
in  grams. 

312 

268 

53 

47 

VI.  Product  from  Large  and  Small  Peas. 


Size. 

No.  of 

peas  in 

188  grms 

No.  of 
plants 
grown. 

Peas  harvested  in  grams. 

Per  area. 

Per  plant. 

384 
530 
780 

360 
505 
680 

2307 
2224 
1590 

6.40 

4.40 

Small 

2.34 

FACTORS  OF  INCREASfi 


Product  of  Large  and  Small  Peas. 


Size  of 

Wt.  of  peas  in  grams 

Wt.  of 
pods  in 
grams 

Wt.  of 
vine  in 
grams 

Proportion 
of  vine 

Seed. 

1st  qual- 
ity. 

2d  qual- 
ity. 

to  fruit 

Large 
Small 

1375 

540 

554 
1045 

1519 
1405 

4185 
4074 

1:0.83 
1:0.76 

Product  of  Large  and  Small  Peas. 


Large 

Medium 

Small 


Aver.  wt. 
of  single 

seeds 
in  grams 


2.73 
2.21 
1.60 


No.  of 
plants 


480 
478 
423 


Wt.  of 

vine 

per  plant 

in  grams 


6.60 
5.50 

4.75 


Wt.  of  peas 
and  pods 
per  plant 
in  grams 


Proportion 
of  vine 
to  fruit 


1:0.71 
1:0.70 
1:0.64 


IX.    Yield  of  Wheat  from  Large  and  Small  Seed. 


Size 
of 
seed 

Weight 

of  straw  in 

grams 

2411 
2211 

Weight 

of  grain  in 

grams 

Proportion 

of  straw  to 

grain 

Large 
Small 

3039 
2456 

1:1.26 
1:1. tl 

LIVING  PLANTS 


X.     Yield  of  Oats  from  Large  and  Small  Seed. 


Size 
of 
seed 

Wt.  of  seeds 

sown  pr.  1000 

in  grams 

Weight 

of  straw  in 

ounces 

Weight 

of  grain  in 

ounces 

Proportion 
of  straw 
to  grain 

Large 
Small 

35.4 
15.9 

556 

518 

190 
143 

1:0.34 
1:0:28 

CHLOROPHYLL  AND  GROWTH.* 

The  adult  leaf  manufactures  about  ninety- 
seven  per  cent  of  the  food  of  the  plant  from 
water  and  carbon  dioxide  of  the  air.  In  the 
study  of  its  functions  and  development  it  is 
of  the  greatest  importance  to  know  whether 
the  plant  can  build  up  a  leaf  from  food  stored 
within  its  body,  or  the  products  of  other 
leaves,  or  whether  the  products  of  the  ma- 
turing leaf  itself  are  necessary  to  enable  it  to 
complete  growth. 

In  recognition  of  this  fact  it  was  one  of  the 
earlier  questions  taken  up  in  the  study  of  the        Historical 
physiology  of  the  plant,  and  it  has  engaged 
the  attention  of  a  number  of  authors  of  the 
first  rank.   It  would  not  be  possible  to  recount 

*Adapted  from  a  lecture  on  "The  Relation  of  the  Growth  of 
Leaves  and  the  Chlorophyll  Function"  before  the  Linnean  So- 
ciety of  London,  Jiine  18,  1896. 


LIVING  PLANTS 


here  the  exact  results  attained  by  each  one, 
except  to  note  that  the  first  investigation  of 
the  subject  was  made  by  de  Saussure  in  1804, 
and  from  his  experiments  upon  leafy  shoots 
of  wood\^  plants  he  was  led  to  assert  that 
leaves  may  not  carry  out  full  development, 
or  maintain  normal  existence  when  the  food- 
forming  processes  were  inhibited.  Subse- 
quently in  dealing  with  various  phases  of  the 
question  Boehm,  Kraus,  Rauwenhoff,  Stebler 
and  Vochting  arrived  at  results  in  harmon^^ 
with  those  of  de  Saussure.  On  the  other 
hand  Batalin,  Vines,  and  Jost  have  reached 
results  quite  to  the  contrary.  Corenwinder 
made  two  series  of  experiments,  one  series  re- 
sulting positively,  the  other  negatively. 

The  experiments  which  would  be  of  value 
in  the  decision  of  this  question  consist  in  al- 
lowing young  leaves  of  many  species  of  plants 
to  develop  under  such  conditions  that  no  food 
can  be  formed. 

To  place  leaves  under  such  conditions  that 
the  chloroph\'ll-bearing  cells  may  not  carry  on 
the  formation  of  food,  and  that  all  growth 
must  be  carried  on  by  means  of  food  brought 
from  a  distant  portion  of  the  plant,  several 
methods  may  be  used,  viz.:  the  leaf  may  be 
enclosed  in  a  dark  chamber  consisting  of  a 
small  box  which  will  exclude  all  rays  of  light 
from  the  leaf,  without  which  the  chloroph3'll 


CHLOROPHYLL  AND  GROWTH 


is  inactive,  or  one  side  of  this  box  may  con- 
sist of  a  sheet  of  blue  glass  which  would 
permit  only  the  blue-violet  rays  to  pass  and 
thus  allow  but  a  small  amount  of  food  to  be 
formed  ;  the  plant  may  be  grown  in  a  substra- 
tum, or  nutritive  solution,  from  which  iron 
salts  have  been  omitted,  and  as  a  consequence 
no  chlorophyll  would  beformed  in  theleaves; 
the  shoot  or  the  entire  plant  may  be  placed  in 
atmosphere  made  free  from  carbon  dioxide  by 
means  of  chemical  reagents.  Of  these  meth- 
ods chief  rehance  is  to  be  placed  upon  those 
in  which  light  is  excluded  from  the  plant,  and 
in  which  carbon  dioxide  is  excluded  from  the 
leaves. 

The  former  method  induces  such  profound 
disturbances  of  the  chemical  processes  and 
regulatory  mechanism  as  to  place  the  plant 
under  highly  pathological  conditions.  The 
more  conclusive  experiments  are  those  by 
which  branches,  or  entire  plants  are  intro- 
duced into  a  sealed  chamber,  which  is  kept 
free  from  carbon  dioxid°  by  means  of  solu- 
tions of  potassium  hydrate,  and  the  ventil- 
ating openings  were  guarded  with  tubulures 
similarly  provided.  The  exact  method  of 
dealing  with  the  plant  may  be  illustrated  by 
the  following  description  of  the  treatment  of 
Arissema  triphyllam. 

The  large  tuberous  corms   were  gathered 


LIVING  PLANTvS 


from  the  soil  in  woods  in  October,  and  placed 
in  a  cold  house  until  February  1st,  when  they 
were  placed  in  a  temperate  room,  beginning 
growth  two  weeks  later.  Ordinarily  the 
plant  sends  up  one  or  two  leaf-stalks  thirty 
to  fifty  centimeters  in  height  bearing  the  tri- 
foliate lamina,  with  an  area  of  one  hundred 
to  two  hundred  and  fifty  square  centimeters 
and  a  scape  twenty  to  forty  centimeters  in 
height,  bearing  a  spadix  enclosed  by  a  hooded 
spathe.  The  hood  contains  a  large  proportion 
of  chlorophyll  and  sustains  in  greater  part 
the  functional  activit^^of  theleaf,  and  exhibits 
similar  reactions  to  light  and  modified  atmo- 
spheres. The  correlation  of  growth  is  such 
that  the  scape  and  inflorescence  attain  full 
size  within  ten  days  from  the  opening  of  the 
bud,  and  the  greater  part  of  the  leaf-expansion 
follows  in  the  next  ten  days.  During  the  first 
ten  days  the  starch  stored  in  the  corm  is  drawn 
upon  to  furnish  an  increasing  amount  of  ma- 
terial for  the  growth  of  the  aerial  organs; 
during  the  next  ten  days  a  decreasing  amount 
is  drawn  from  the  corm,  and  usually  after 
that  time  a  stream  of  plastic  material  sets  in 
the  opposite  direction  from  the  laminae,  which 
is  in  part  stored  in  the  corm  and  in  part  used 
in  the  development  of  the  lateral  offshoots, 
which  begin  development  at  this  time. 
Buds  which  had  attained  the  height  of  ten 


CHLOROPHYLI.  AND  GROWTH  125 

cm.  were  brought  through  an  opening  in  a 
glass  plate  allowed  to  rest  upon  the  top  of 
the  pot  in  which  the  plant  was  grown.  The 
opening  around  the  bud  was  securely  sealed 
by  means  of  wax,  molding  clay,  or  the  fol- 
lowing device:  A  cork  stopper  was  perfor- 
ated with  an  opening  larger  than  the  ulti- 
mate size  of  the  sheathing  petioles,  and  the 
upper  part  of  the  opening  was  enlarged  to 
form  a  cup-shaped  cavity.  After  the  cork  had 
been  saturated  with  paraffin  it  was  placed  in 
the  glass  plate  and  enclosing  the  bud,  the 
bottom  of  the  cup-shaped  cavitj' covered  with 
a  loose  layer  of  asbestos  or  glass-wool,  and 
over  this  was  poured  a  layer  of  mercury  five 
millimeters  in  thickness,  which  was  covered 
with  water  to  prevent  injurious  action  of  the 
metal. 

This  method  of  sealing  exerted  no  harmful 
pressure  on  the  plant  and  allowed  it  to  ex- 
pand in  a  normal  manner— a  very  important 
consideration  in  experiment  where  soft- 
stemmed  herbaceous  plants  were  used.  The 
plants  were  covered  with  a  bell-jar  of  a  capac- 
ity of  four  to  eight  liters  sealed  to  the  glass 
plate,  and  provided  with  two  tubulures.  To 
one  tubulure  was  fitted  a  series  of  potassium 
tubes  or  vessels  containing  potassium  hy- 
drate in  solid  form,  and  saturating  a  mass  of 
asbestos  fiber.     The  second  tubulure  was  con- 


LIVING   PLANTS 


Fig.  12.— Apparatus  for  growing  plants  in  an  atmosphere 
free  from  carbon  dioxide:  1.  Dish  containing  solution  of  jio- 
tassium  hydrate.  2.  Specimen  of  Aiisiema  triiihylhnn  10 
days  after  opening  of  bud.  3.  Receiver  of  10  liters  capacity. 
4..  Outlet-tube  connected  with  aspirator.  5.  Sticks  of  potas- 
sium hydrate  and  moist  asbestos  fiber.  6-9.  Detail  of  method 
for  sealing  plant  in  receiver.  6.  Cork.  7.  Asbestos  fiber. 
8.  Mercury.  9.  Stem  of  plant.  10.  Sponge  saturated  with 
water. 


CHLOROPHYLL  AND  GROWTH 


iiected  with  an  aspirator,  by  which  the  air  was 
occasionally  renewed.  Several  vessels  con- 
taining two  to  five  grams  of  solid  potassium 
hydrate  were  placed  inside  of  the  bell-jar. 
The  potassium  absorbed  water  rapidly  and 
soon  dissolved.  To  provide  against  the  dry- 
ness of  the  inclosed  air  thus  induced  a  large 
sponge  saturated  with  water  was  placed  near 
the  plant.  These  precautions  furnish  normal 
conditions  except  in  the  composition  of  the 
air,  from  which  almost  all  of  the  carbon  diox- 
ide is  taken.  It  is  of  course  understood  that 
the  plant  is  constantly  giving  off  this  sub- 
stance as  a  result  of  its  oxidation  processes, 
and  it  may  be  imagined  as  forming  a  diffuse 
stream  from  the  plant  to  the  vessels  contain- 
ing the  potassium  solutions.  The  amount  ac- 
tually present  in  the  bell-jar  at  any  time  how- 
ever must  have  been  quite  small.  The  potas- 
sium solutions  were  renewed  once  each  week. 
Plants  of  Arisaema  grown  in  the  apparatus 
described  above  exhibited  a  normal  develop- 
ment during  the  opening  of  the  bud,  and  the 
preliminary  stages  of  the  unfolding  of  the 
leaves,  which  are  crumpled  in  the  bud  during 
a  period  of  two  to  four  days.  The  develop- 
ment process  was  arrested,  how^ever,  at  a 
very  early  stage,  and  the  laminte  were  un- 
folded only  so  far  as  to  expose  the  ventral  sur- 
face,  and  the  crumpled  appearance  was  not 


Growth  in  the 
absence  of 
carbon  dioxide 


LIVING  PLANTS 


lost.  In  ten  to  fourteen  days  after  the  begin- 
ning of  the  experiment,  the  laminae  assumed 
a  yellowish  color,  as  a  result  of  the  decom- 
position of  the  chlorophyll,  and  other  signs  of 
deterioration  appeared  ending  in  the  death  of 
the  organ  a  few  days  later. 

The  structure  and  arrangement  of  the  tis- 
sues had  undergone  but  little  differentiation 
from  the  forms  present  in  thefolded condition, 
and  differed  from  the  normal  forms  by  thesize 
of  the  single  layer  of  palisade  cells  and  the 
globular  form  of  the  spongy  parenchyma,  and 
seemed  moreover  to  be  in  a  state  of  hunger. 
It  is  to  be  noted  that  the  sheathing  spathe 
also  undergoes  similar  abnormalities,  but 
since  it  is  never  folded,  and  since  its  develop- 
ment consists  principally  of  a  longitudinal  ex- 
pansion of  the  cylindrical  sheath  and  hooded 
tip,  the  more  apparent  deviation  is  one  of  size. 
The  thickness  is  such  as  to  prevent  crumpling. 
It  is  to  be  noted  moreover  that  the  develop- 
ment of  the  spathe  is  usually  accomplished 
before  the  leaves  have  begun  maximal  growth 
under  normal  conditions.  If  mature  leaves 
were  sealed  into  an  apparatus  similar  to  the 
above,  no  changes  were  discernible  until  fif- 
teen to  twenty  days  later.  At  this  time  the 
starch,  and  other  carbohydrates  with  which 
they  were  richly  loaded,  having  been  used,  a 
shrinkage  was  noticeable  and   the  leaf  was 


CHLOROPHYLL  AND  GROWTH 


found  to  be  in  a  state  of  hunger.    On  restor- 


FlG.  13. — AriScEma  triphyllum  grown  in  open  air. 

ation  to  a  normal  atmosphere  before  decay 


LIVING  PLANTS 


had  begun  they  were  restored  to  a  normal 
condition. 

In  order  to  cultivate  plants  in  darkness  but 
under  otherwise  approximately  equal  condi- 
tions, a  bottomless  chamber  of  galvanized  iron 
was  constructed,  and  allowed  to  rest  on  a 
metal  bench  covered  with  a  layer  of  moist 
sand.  This  dark  chamber  was  placed  in  such 
position  that  the  sun's  rays  did  not  strike  it, 
and  was  attached  to  a  simple  pulley,  by 
which  it  might  be  raised  and  lowered  to  allow 
an  occasional  examination  of  the  plants. 

Awakening  plants  with  corms  five  centime- 
ters long,  when  placed  in  this  chamber, 
showed  a  greatly  exaggerated  development 
of  the  bud  scales,  a  rapid  elongation  of  the 
scapes  and  petioles  attaining  a  length  near- 
ly double  the  normal  in  five  to  eight  days. 
The  daily  increase  of  these  organs  in  some 
instances  amounted  to  twelve  centimeters. 
The  laminae  sometimes  were  carried  com- 
pletely or  almost  completely  through  the  un- 
folding stage,  but  were  rarely  able  to  attain 
a  full  extension,  or  area,  much  in  excess  of  the 
folded  condition,  andowingto  the  absence  of 
the  directive  influence  of  light,  assumed  var- 
ious positions  with  respect  to  the  horizontal. 
Effect  of  'pj^g  process  of  decay  did  not  begin  until  fifteen 

to  twenty  days  after  the  beginning  of  the  ex- 
periments, and  if  the  plants,  after  unfolding, 


darkness 


CHLOROPHYLL  AND  GROWTH 


were  brought  into  diffuse  light  with  gradually 
increasing  intensity,  the  normal  appearance 

was    fi- 
nally 
resum- 
ed. The 
color  of 
the  eti- 
olated 
leaves  was  of  the  cus- 
tomary waxy  yellow, 
pon  which  the  rtddish  pur- 
ple color  areas  characteris- 
tic  of    the  external    tissue 
were  boldly  apparent.    The 
spathe  exhibited  great  vari- 
ety of  reaction,  but  in  gen- 
eral it  did  not  attain   full 
development.       This  was 
the  invariable  result  if  this 
member  alone  was  enclosed 
in  a  covering   excluding 
light.       And  although  not 
responsive  to  the  directive 
action  of  light  or  gravity, 
it  assumed   an   upright  or 
outwardly    recurved    posi- 
tion in  darkness. 
If    plants    with    mature 
leaves  were  placed  in  the  dark  chamber  a  re- 


FlG.  14. — Arissema  tri 
phyllum  grown  in  an  at 
mosphere  free  from  car 
bon  dioxide. 


LIVING  PLANTS 


newed  activity  of  the  petioles  occurred,  last- 
ing two  to  three  days,  and  in  four  or  five 
days  the  laminae  began  to  bleach  and  decay. 

Plants  grown  in  a  diffuse  hght  exhibited 
features  of  development  in  general  analogous 
to  those  shown  in  darkness.  Elongation  of 
the  petioles,  and  scape,  and  dwarfing  of 
the  spathe  especially  of  the  overarching  hood 
occurred.  Still  more  marked,  however,  was 
the  restriction  of  the  area  of  the  laminae,  cor- 
responding to  the  intensity  of  the  light. 

In  order  to  determine  how  far  the  diversion 
of  food  from  certain  members,  and  its  concen- 
tration in  one  might  affect  its  development, 
recourse  was  had  to  the  removal  of  two  of 
the  three  aerial  members  of  plants  grown  in  a 
dark  chamber.  If  the  leaves  were  removed  no 
changes  resulted  in  the  development  of  the 
scape  or  spathe.  The  latter  organ  was 
dwarfed,  although  not  more  than  thirty  cen- 
timeters from  the  stored  food  in  thecorm.  If 
the  scape  and  one  leaf  were  removed  from  a 
plant  emerging  from  the  bud  in  a  dark  cham- 
ber, the  remaining  leaf  exhibited  a  develop- 
ment quite  similar  to  those  of  entire  plants 
under  similar  circumstances,  except  that  the 
petiole  reached  a  length  much  in  excess  of 
those  on  an  entire  plant.  The  laminae  were 
extended  in  such  manner  as  to  cause  the  dis- 
appearance of  the  angles  of  the  leaf-folding  in 


CHLOROPHYLL  AND  GROWTH 


Fig.    15.  — ArisiL-ma 
phylluin  grown  in  dark] 


the  bud.      They  soon 
became    recurved    at 
the  margins,  and  only  a 
small  increase  in  size  oc- 
curred after  unfolding. 

The  removal  of  one 
leaf  and  the  scape,  from 
plants  grown  in  an  air 
free  from  carbon  dioxide, 
resulted  in  a  somewhat 
more  complete  develop- 
ment of  the  laminte  than 
in  an  entire  plant  under 
the  same  circumstances. 
The  angles  taken  on  in 
the  bud  completely  dis- 
appeared, an  approxi- 
mately normal  green  col- 
or, and  a  position  quite 


134 


LIVING  PLANTS 


Total  results 
with  Arisaema 


similar 
of 

in  free 
assum- 
The  a- 
of  food 

able  for  devel- 
have  been  two 
great  as  that 
single  leaf.  In 
days,  however, 
to  exhibit  signs 
but  if  at  this 
moved  from  the 
placed  in  the 
m  a  1  condition 
development 
usual  manner, 
the  result  of  the 
ments  that  the 
plant  of  Arisae- 
of  development, 
ing  stage  in  an 
from  carbon  di- 
the  three  aerial 
moved,  the  re- 
attain  a  more 
developmen  t. 
tioles  are  great- 
the  laminae    un- 


to that 
plan  ts 
air  was 
ed. 

mount 
avail- 
o  p  m  e  n  t  m  u  s  t 
or  three  times  as 
usually  afforded  a 
twelve  to  fourteen 
the  laminae  began 
o  f  deterioration  ; 
time  they  were  re- 
apparatus  and 
open  air  the  nor- 
was  regained  and 
proceeded  in  the 
It  is  to  be  seen  as 
foregoing  ex  peri - 
leaves  on  an  entire 
ma  are  incapable 
beyond  the  unfold- 
atmosphere  free 
oxide.  If  two  of 
members  are  re- 
maining one  ma}' 
advanced  stage  of 
In  darkness  the  pe- 
ly  elongated,  and 
fold,  but  no  expan. 


Fig.  16. — Arisaema  triphyllum   with  flower  stalk   and   one 
leaf  ctit  away,   in   an   atmosphere  free  from   carbon  dioxide. 


CHLOROPHYLL  AND  GROWTH 


sion  of  their  area  ensues.  The  removal  of 
concurrent  members  results  in  an  exaggerat- 
ed extension  of  the  petiole,  but  has  no  effect 
on  the  laminae.  A  similar  result  is  obtained 
with  the  spathe  under  both  conditions.  It 
is  to  be  noted  that  in  light  the  removal  of 
concurrent  organs  results  in  an  increased 
development  of  the  laminae,  and  in  darkness 
of  the  petiole. 

Calla  palustris  is  a  plant  consisting  of  a 
creeping  rhizome  one  to  two  centimeters  in 
thickness,  from  the  apex  of  which  arise  a  few 
cordate  leaves  with  petioles  fifteen  to  twenty 
centimeters  long  and  one  or  more  solitary 
scapes  eight  to  fifteen  centimeters  high.  The 
relatively  large  rhizomes  are  filled  with  stored 
food. 

Plants  brought  into  a  warm  house  and 
placed  under  the  apparatus  described  above 
exhibited  a  development  of  the  petioles  and 
laminae  during  a  period  of  ten  to  twelve  days 
that  resulted  in  the  formation  of  perfect  leaves. 
The  continued  existence  of  the  plant,  however, 
under  such  conditions  was  impossible  because 
of  the  destruction  of  the  stored  food  by  fer- 
mentation. 

In  the  dark  chamber  the  slight  extension  of     Results 
the  petioles  occurred  while  the  laminge  attained     with  Calla 
a  size  equal  to  those  in  the  open  air,  although 
they  were  recurved  at  the  margins.   No  effects 


LIVING  PLANTS 


were  obtained  by  the  removal  of  the  concur- 
rent members. 

Seedlings  of  Zeamais,  with  theshoot  emerg- 
ing from  the  cotyledon,  were  placed  entirely 
inside  of  the  apparatus,  where  they  remained 
for  a  period  of  eight  to  twelve  days  without 
carbon  dioxide.  In  such  experiments  the 
plant  evidently'  could  carry  on  the  extension 
of  the  shoot  only  so  long  as  food  could  be  ob- 
tained from  the  seed.  To  determine  the  ac- 
tual constructive  value  of  the  stored  food 
in  the  seed,  plants  were  allowed  to  remain  in 
the  apparatus  until  the  leaves  exhibited  indi- 
Resuhs  cations  of  deterioration,  which  was  eleven  to 

with  Zea  fourteen  days  after  the  beginning  of  the  exper- 

iment. The  plants  were  more  slender  and  the 
leaves  narrower  than  in  control  plants.  A 
small  amount  of  starch  was  still  to  be  ob- 
served in  the  seeds,  both  in  the  plants  grown 
in  the  air  free  from  carbon  dioxide  and  in 
normally  grown  plants  of  the  same  age. 

In  darkness  the  stems  are  elongated  and  the 
etiolated  leaves  are  much  narrower  than  in 
normal  plants. 

Specimens  of  Phoenix  dactylifera  were  ob- 
tained by  the  germination  of  the  seeds  of  the 
commercial  date,  a  process  requiring  from 
twenty  to  thirty  days.  The  seed  consists 
largely  of  reserve  cellulose,  and  according  to 
Haberlandt  is  sufficient  to  allow  the  forma- 


CHLOROPHYLL  AND  GROWTH 


tion  of  a  primary  root  more  than  a  meter  in 
length,  before  the  unfolding  of  the  first  foliage 
leaf  in  the  natural  habitat  of  the  plant.  In 
jjlanting  the  seeds  in  moist  soil  this  excessive 
development  of  the  roots  was  useless,  and 
foliage  leaves  began  to  unfold  when  the  root 
had  attained  a  length  of  a  few  centimeters. 

The  seedlings  grown  in  small  pots  were 
placed  inside  the  apparatus  and  kept  free  from  j^gg^j^g 
carbon  dioxide  for  a  period  of  thirty  to  forty  ^^^  Phoenix 
days.  The  leaves,  which  at  the  beginning  of 
the  experiment  were  emerging  from  the  sheath- 
ing scale,  exposing  a  tip  one  to  two  centi- 
meters in  length,  attained  a  length  of  fifteen 
centimeters  and  a  complete  normal  expansion 
corresponding  to  that  of  organsgrown  in  the 
open  air.  Such  leaves  usually  attain  a  length 
of  twenty  to  thirt}'  centimeters  by  a  slow 
process  of  growth  lasting  several  months,  and 
my  experiment,  therefore,  covers  only  the 
earlier  stages  of  development. 

Specimens  placed  in  a  dark  chamber  during 
a  period  of  thirty  to  forty  days  exhibited  an 
exaggerated  elongation  of  the  cotyledonary 
and  leaf  scales,  as  well  as  the  leaf  itself,  which 
retained  its  lamina  in  the  plicately  folded 
position.  The  increase  in  length  amounted 
to  twentv  to  thirty  per  cent  more  than  in 
control  plants. 

It  is  safe  to  conclude  that  the  development 


LIVING  PLANTS 


of  seedlings  of  corn  and  date  may  proceed 
so  long  as  the  necessary  amount  of  plastic 
material  is  available. 

In  such  manner  many  specimens  each  of 
Arissema  triphyllum,  Calla  palustris,  Lilium 
splendkJum,  Trillium  erectum  and  T.  erythro- 
carpum,  Isopyrutn  biternatum,  Oxalis  £ori- 
hunda  and  O.  vespertilionis,  Justitia  sp.,  Hi- 
biscus rosa-sinensis,  Zea  tnais  and  Phoenix 
dactylifera  were  grown.  Of  these  it  was 
found  that  leaves  of  Ariscema  perish  in  an  air 
free  from  carbon  dioxide  at  the  beginning  of 
the  unfolding  stage;  leaves  of  Calla,  Lilium 
and  Trillium  attain  normal  stature  but  are 
incapable  of  further  existence.  Leaves  of  Zea 
carry  on  normal  development  during  a  period 
often  to  twelve  days,  but  in  this  time  attain 
each  a  stature  inferior  to  that  of  control 
plawts,  and  then  begin  to  deteriorate.  Leaves 
of  Oxalis,  Isopyrum,  Hibiscus,  and  Justitia 
attained  normal  stature,  and  were  capable  of 
continued  existence  at  the  expense  of  food  de- 
rived from  storage  tracts,  or  active  chloro- 
phyll-bearing tissues. 

In  the  ordinary  course  of  leaf  development 
growth  is  carried  from  the  rudimentary  stage 
to  the  unfolding  of  the  lamina  at  the  expense 
of  food  derived  from  storage  organs  or  from 
the  main  axis.  Ordinarily  the  supply  of  food 
transported  to  the  developing  leaf  is  supple- 


CHI.OROPHYLL  AND  GROWTH 


men  ted  early  in  the  unfolding  stage,  by  food 
formed  by  the  young  lamina.  In  a  short  time  odinary  c 
the  supplementary  amount  from  the  leaf  is  of  growth 
entirely  sufficient  for  its  own  needs  for  con- 
structive purposes ;  and  at  this  time  the  re- 
serve food  transported  to  the  leaf  has  under- 
gone great  diminution.  When  a  leaf  is  placed 
under  such  conditions  that  the  lamina  is  inac- 
tive, the  amount  of  reserve  material  which 
can  be  transported  to  the  leaf  will,  in  many 
instances,  be  found  insufficient  for  its  needs. 
This  will  be  best  understood  when  it  is 
stated  that  the  amount  used  at  this  time  is 
many  times  greater  than  that  needed  in  the 
earlier  stages,  and  moreover,  that  the  difficul- 
ties of  translocation  have  vastly  increased. 
Thus  by  the  elongation  of  the  petioles — 
amounting  from  two  to  ten  centimeters  daily 
in  Arisaema — the  distance  between  the  stored 
food  in  thecorm  and  the  point  of  consumption 
in  the  leaf-blade  has  been  greatly  exaggerated. 
Then  again  the  amount  of  stored  food  has 
been  materially  reduced  by  consumption  and 
the  intervention  of  destructive  fermentations. 
It  is  apparent  without  recourse  to  a  further 
recital  of  the  detail  of  the  experiments,  that, 
if  at  a  time  when  the  available  food  supply  is 
diminishing  to  a  minimum,  and  the  difficulties 
attendant  on  translocation  are  becoming 
greater,  the  needs  of  the  leaf  should  suddenly 


LIVING  PLANTS 


mount  to  a  maximum,   the  supply  may  be 
found  insufficient,  unless  supplanted  by  the 
food-forming  activity  of  the  lamina,  and  de- 
terioration of  the  tissues,  due  to  starvation, 
must  ensue. 
The  stage  in  which  the  translocated  food 
Growth  with    becomes    inadequate  is  not    identical   in  all 
insufficient       species.      Thus  it   appears    from   my  experi- 
nutrition  nicnts  that  relatively  small  leaves,   or   those 

with  less  rapid  development,  or  with  a  read- 
ily available  supply  of  food  material,  may 
attain  a  much  more  advanced  stage  than 
those  in  which  the  contrary  conditions  pre- 
vail. The  conditions  may  be  so  favorably 
disposed  as  to  allow  not  only  of  the  complete 
development  of  the  leaf,  but  also  of  its  contin- 
ued maintenance  under  conditions  of  func^ 
tional  inactivitv  with  respect  to  the  chloro- 
phyll. 

It  is  to  be  noted  that  the  phrase,  "function- 
al inactivity,"  is  used  in  a  relative,  not  an 
absolute  sense.  The  portion  of  the  plant  en- 
closed in  the  apparatus  is  constantly  emitting 
carbon  dioxide ;  which  is  rapidly  absorbed  by 
the  potassium  solutions.  Under  such  circum- 
stances the  carbon  dioxide  may  be  imagined 
as  forming  a  diffuse  stream  from  the  plant  to 
the  potassium,  and  the  amount  actually 
available  by  the  chlorophyll-bearing  cells  at 
any  one  time  must  be  extremely  small.     Some 


CHLOROPHYLL  AND  GROWTH 


doubt  still  exists  as  to  the  cause  of  the  rapid 
deterioration  of  inactive  leaves.  It  is  held  by 
some  that  it  is  due  to  the  harmful  substances 
set  free  in  the  decomposition  of  chlorophyll, 
while  it  is  asserted  on  the  other  hand  that  the 
breaking  up  of  the  chlorophyll  is  a  result  of 
starvation  and  functional  inactivity. 

Finally  it  may  be  said  that  in  order  to  ac- 
count for  the  reactions  of  inactive  leaves  in 
light  and  in  darkness  it  is  necessary  to  predi- 
cate the  intervention  of  the  regulatory  mech- 
anism in  a  manner  almost  entirely  specific. 
Such  action  has  been  described  in  Arisaema, 
which  on  the  removal  of  concurrent  members, 
develops  laminae  in  the  light  and  petioles 
in  darkness.  That  is  to  say,  it  should  not  be 
taken  for  granted  that  all  of  the  changes  de- 
scribed in  the  above  plants  are  due  simply  to 
disturbances  of  the  nutritive  processes,  but 
represent  to  some  extent  an  irritable  response 
ofthe  plant  to  the  unusual  conditions  under 
which  it  is  placed  and  from  which  it  attempts 
to  free  itself  Thus  the  excessive  elongation 
of  the  stems  and  petioles  in  darkness  seems 
very  clearly  an  adaptive  modification  for  lift- 
ing the  leaf-blades  and  chlorophyll  out  of  ob- 
scurity and  into  sunlight,  and  may  not  be 
accounted  for  on  an^^  other  grounds.  (This 
theory  of  elongation  as  an  adaptive  modi- 
fication was  originally  proposed  by  Godlew- 


LIVING  PLANTS 


ski  in  1873.)  The  results  of  the  foregoing 
discussion  may  be  briefly  summarized  in  the 
following  paragraphs. 

The  relation  of  the  growth  of  leaves  to  their 
Conclusions  food-forming  power,  is  such  that  some  are 
able  to  carry  development  no  further  than 
the  beginning  of  the  unfolding  stage  of  the 
laminae ;  others  are  able  to  carry  the  develop- 
ment to  an  approximately  normal  stature; 
and  others  are  capable  not  only  of  the  devel- 
opment to  normal  stature  but  also  of  con- 
tinued maintenance  under  conditions  of  en- 
forced inactivity. 

This  varying  reaction  of  leaves  is  dependent 
upon  a  series  of  conditions  which  may  be  in- 
cluded in  the  phrase  "availability  of  the  food 
supply." 

The  deterioration  of  certain  leaves  under 
conditions  of  forced  inactivity  is  due  to  insuf- 
ficient nutrition  and  is  accompanied  by  the 
disintegration  of  the  chlorophyll. 

The  behavior  of  inactive  leaves  in  light  ex- 
hibits no  similarities  or  correspondence,  in 
simple  growth  or  upon  the  intervention  of 
correlation  processes,  to  their  behavior  in 
darkness. 

Material  constructed  in  active  chlorophyll 
areas  and  stored  in  special  organs  may  be 
transported  to  inactive  chloroplndl-bearing 
organs  in  some  plants  in  light  and  in   dark- 


CHLOROPHYLL  AND  GROWTH 


ness,  and  be  used  in  such  manner  as  to  allow 
of  the  perfect  development  of  these  organs. 

The  removal  of  concurrent  members  in  dark- 
ness may  have  no  effect,  may  cause  an  exag- 
gerated development  of  the  petioles,  or  may 
result  in  the  perfect  development  of  the  entire 
leaf.  The  nature  of  the  regulatory  mechanism 
in  each  instance  is  entirely  specific. 

It  is  possible  for  some  plants  to  form  perfect 
leaves  in  darkness,  when  some  of  the  branch- 
es only  are  darkened,  and  for  others  when 
the  entire  plant  is  etiolated.  It  is  thus  shown 
that  no  invariable  connection  exists  between 
the  phototonic  condition  and  leaf-develop- 
ment. 

Placing  a  leaf  under  such  conditions  that 
it  cannot  construct  food  sets  in  motion 
the  specific  regulatory  mechanism  of  the  or- 
ganism in  such  a  manner  that  the  plastic 
material  may  be  withdrawn,  and  the  organ 
cast  off.  An  exaggerated  development  of  the 
petioles  may  be  induced  in  darkness  by  this 
mechanism. 

The  excessive  elongation  of  the  stems  and 
petioles  in  darkness  is  to  be  regarded  as  a 
phenomenon  of  adaptation  by  which  the 
leaf  surfaces  would  be  placed  beyond  any  ob- 
ject intervening  between  them  and  the  light. 


LEAVES  IN  SPRING,  SUMMER  AND  AUTUMN.* 

The  yearly  miracle  of  the  appearance  of  in- 
numerable shades  and  hues  of  green  in  awak- 
ening vegetation ,  exerts  a  mysterious  influence 
amounting  to  fascination  over  the  human 
race.  A  fascination  made  strong  by  the  in- 
herited experience  of  untold  generations  of 
forest-dwelling  ancestors,  reaching  backward 
the  entire  present  geologic  period,  and  which 
grows  in  intensity  as  we  creep  from  the  crea- 
tion to  millenium. 

Our  vague  and  emotional  inherited  interest 
in  the  annual  revivification  of  the  vegetable 
world  becomes  vividly  intense  and  direct, 
however,  when  it  is  learned  that  the  universal 
blush  of  green  is  due  to  the  most  important 
coloring  substance  in  the  world — chlorophyll. 

^'Adapted  from  "Green  Color  of  Plants,"  Harper's  Magazine, 
April,  1897,  and  "Autumn  Leaves,"  same  joxirnal,  October, 
1897. 


.IVING  PLANTS 


It  is  literally  true  that  the  existence  of  every 
living  thing  is  ultimately  dependent  upon  the 
activity  of  plant-green. 

The  actual  conditions  are  as  follows :  the 
elements  which  enter  into  the  construction  of 
protoplasm  are  carbon,  nitrogen,  oxygen, hy- 
drogen and  phosphorus.  These  elements  are 
found  in  the  form  of  free  gases  or  simple  com- 
pounds in  the  soil  and  atmosphere,  and  can- 
not be  used  by  protoplasm  until  built  up  into 
the  form  of  complex  compounds.  The  con- 
struction of  compounds  indispensable  for  the 
nutrition  of  plants  and  animals  does  not  re- 
Importance  of  suit  from  mere  proximity  of  the  elements, 
chlorophyll  since  those  most  highly  desirable  are  chem- 

ically inactive  to  one  another,  and  will  unite 
only  under  the  influence  of  energy  from  with- 
out. The  substances  are  selected  and  ab- 
sorbed in  their  elemental  condition  by  the 
plants,  and  in  the  crucible  of  the  cell,  glowing 
with  potentiality  absorbed  from  sunhght,are 
fused  together  and  made  ready  for  assimila- 
tion by  protoplasm. 

The  most  important  synthetic  process  is 
that  which  results  in  the  formation  of  carbon 
hydrates  from  carbon  dioxide  and  water.  If 
this  process  were  carried  on  b3^  means  of  en- 
ergy furnished  by  the  activity  of  the  proto- 
plasm, the  expenditure  entailed  would  over- 
balance the  benefits  gained  by  the  assimilation 


LEAVES  IN  SEASONS 


of  the  substances  formed.  It  is  clearly  ap- 
parent, therefore,  that  the  organism  must 
receive  energy  from  some  external  source  and 
must  be  able  to  convert  this  energy  into  the 
forms  necessary  to  promote  chemical  synthe- 
sis. Sunlight  is  a  universal  source  of  energy 
and  green  plants  are  the  onlj^  organism  capa- 
ble of  converting  its  rays  into  available  ener- 
gy. The  transformation  is  effected  by  means 
of  chlorophyll. 

It  is  true  that  a  few  lower  forms,  inclusive 
of  the  "sulphur"  and  "iron"  bacteria  among 
plants  and  some  of  the  lower  forms  among 
animals,  are  able  to  accomplish  the  construc- 
tion of  carbohydrates,  but  the  total  result 
of  their  activity  is  indefinitely  unimportant, 
and  is  doubtless  at  the  cost  of  energy  furnish- 
ed by  complex  compounds  derived  from  other 
plants  and  animals. 

Animals  and  non-green  plants  are  therefore 
dependent,  directly  or  indirectly,  upon  the 
substances  formed  by  the  green  plants  for 
food.  This  physiological  characteristic  has 
led  a  recent  German  writer  to  classify  the 
fungi  (mushrooms,  toadstools,  molds,  etc.) 
among  animals.  A  classification  that  would 
work  privation  to  the  vegetarian  if  seriously 
accepted . 

The  action  of  chlorophyll  may  best  be  un- 
derstood  when  its    physical    properties    are 


LIVING  PLANTS 


demonstrated.  In  order  to  do  this  a  solution 
of  the  substance  is  obtained  by  placing  a 
gram  of  chopped  leaves  of  grass  or  geran- 
ium in  a  few  cubic  centimeters  of  alcohol  for 
an  hour.  The  solution  will  be  a  bright,  clear 
green  color,  and  when  the  vessel  containing  it 
is  held  in  such  a  manner  that  the  sunlight  is 
Properties  of  reflected  from  the  surface  of  the  liquid  it  will 
chlorophyll  appear  blood-red,  due  to  its  property  of  )?wor- 

escence,  that  of  changing  the  wave  lengths  of 
the  violet  end  of  the  spectrum  in  such  a  man- 
ner as  to  make  them  coincide  with  those  of 
the  red  end.  It  is  by  examination  of  light 
which  has  passed  through  a  solution  of  chlor- 
ophyll, however,  that  the  greatest  insight 
into  its  physical  properties  may  be  obtained. 
If  such  a  ray  is  passed  through  a  prism  and 
spread  upon  a  screen,  it  may  be  seen  that 
there  are  several  intervals  of  dark  bands  in 
the  spectrum.  The  rays  which  would  have 
occupied  these  spaces  have  been  absorbed  by 
the  chlorophyll  and  converted  into  heat  and 
other  forms  of  energy.  This  energy  is  directly 
available  to  the  protoplasm  containing  the 
chlorophyll.  As  a  necessary  concomitant  of 
its  physical  properties,  chlorophyll  is  usually 
only  to  be  found  in  organs  exposed  to  the 
light.  It  would  not  only  be  useless  but  dan- 
gerous elsewhere,  as  it  disintegrates  in  dark- 
ness into  substances  hurtful  to  the  organism. 


LEAVES  IN  SEASONS 


It  is  found  in  greatest  quantity  in  leaves  in 
layers  of  special  cells  beneath  the  epidermis. 
It  is  not  distributed  throughout  the  entire 
cell,  but  occurs  in  the  masses  of  protoplasm 
which  the  botanist  terms  chloroplasts.  The 
chloroplasts  are  sponge-like  structures,  and 
the  chlorophyll  is  to  be  found  in  solution  in 
an  oil  in  the  interstices  of  the  protoplasmic 
sponge. 

Chlorophyll  is  an  extremely  complex  sub- 
stance and  correspondingly  unstable.  Hence 
as  soon  as  the  chemist  extracts  it  from  the 
plant  in  the  attempt  to  make  an  analysis, 
disintegration  sets  in  and  he  is  no  longer 
dealing  with  chlorophyll,  but  with  the  sub- 
stances derived  from  it  by  decomposition. 
Investigation  upon  the  nature  and  activity 
of  plant-green  has  been  in  progress  more  than 
a  century,  yet  its  exact  chemical  composition 
is  unknown.  It  contains  carbon,  oxygen, 
hydrogen,  nitrogen,  magnesium  and  phos- 
phorus, but  the  proportions  and  arrangement 
of  the  atoms  of  each  element  in  the  molecule 
of  chlorophyll  have  not  been  exactly  ascer- 
tained. 

The  beautiful  and  striking  colors  of  autum- 
nal foliage  are  due  in  greater  part  to  sub- 
stances formed  by  the  disintegration  of  chlo- 
rophyll. The  many  thousands  of  tints  of 
green  leaves  are  due  to  a  number  of  causes. 


LIVING  PI.ANTvS 


In  some  cases  the  outer  layers  of  cells  of  the 
the  leaf,  or  merely  the  walls  of  the  cells,  may 
contain  coloring  matter.  The  number  and 
size  of  the  chloroplasts,  and  consequently  the 
amount  of  the  chlorophyll,  may  be  greater  in 
some  leaves  than  in  others.  Besides,  the  chlo- 
Varying  tints  roplasts  may  be  moved  about  in  the  cell  and 
their  distance  from  the  surface  of  the  leaf 
altered,  or  they  maybe  placed  in  lines  perpen- 
dicular or  parallel  to  the  surface.  In  this 
manner  the  infinite  and  elusive  variations  of 
color,  so  fascinating  to  the  lover  of  nature, 
are  produced  in  vegetation.  The  color  of  a 
leaf  may  vary  momentarily  throughout  the 
day,  as  indeed  does  that  of  the  entire  land- 
scape to  the  puzzled  artist. 
The  cell  sap  which  bathes  thechloroplast  in 
Synthesis  the  leaves  contains  carbon  dioxide  absorbed 

o^  ^°°^  from  the  air.     When   the  sun   shines  upon  a 

leaf  the  rays  pass  through  the  epidermis  and 
penetrate  the  cells  containing  the  chloroplasts. 
The  chlorophyll  converts  a  large  proportion 
of  the  light  into  heat  nnd  other  forms  of  en- 
ergy. With  this  energy  as  a  motive  power 
the  protoplasm  of  the  chloroplast  withdraws 
water  and  carbon  dioxide  from  the  surround- 
ing cell  sap  and  combines  them  in  such  man- 
ner that  a  substance  known  as  formic  alde- 
hyde is  formed  and  oxygen  is  liberated.  In 
a  second   stage    the   atoms    of  carbon,    hy- 


LEAVES  IN  SEASONS 


drogen  and  oxygen  in  six  molecules  of 
formic  aldehyde  are  rearranged  in  one  com- 
plex molecule  forming  sugar,  from  which  the 
other  carbohydrates  are  easily  derived.  Pro- 
toplasm may  not  be  formed  from  sugar  alone, 
since  nitrogen  is  a  very  important  constituent 
of  living  substance.  It  is  probable  that  nitro- 
genous substances  are  sometimes  formed  by  a 
variation  in  the  earlier  stages  of  the  process 
described  above,  by  which  nitrogen  is  substi- 
tuted for  oxygen  in  the  molecule  of  formic 
aldehyde.  Such  a  substitution  would  result 
in  the  formation  of  hydrocyanic  acid.  The 
recent  discovery  of  this  deadly  acid  in  the 
leaves  of  a  tropical  palm  lends  favor  to  the 
hypothesis.  It  may  be  formed  in  many  green 
leaves,  but,  like  the  earlier  substances  in  the 
synthesis  of  sugar  may  undergo  instant  trans- 
formation and  thus  escape  detection. 

The  absorption  of  carbon  dioxide  from  the 
air,  and  the  excretion  of  oxygen  by  vegeta- 
tion is  sufficient  to  balance  the  opposite 
process  in  animals,  and  hence  thecomposition 
of  the  atmosphere  remains  unchanged.  It  is 
a  notable  fact  that  plants  thrive  in  an  atmo- 
sphere containing  a  much  larger  proportion 
of  carbon  dioxide  than  is  found  in  the  atmo- 
sphere at  the  present  time.  Normal  air  con- 
tains but  one-twenty-lifth  of  one  per  cent  of 
this  gas,  and  the  food-forming  power  of  the 


LIVING  PLANTS 


chlorophyll 


plant  is  greatest  in  an  atmosphere  containing 
two  hundred  times  as  much,  seven  to  ten  per 
cent  by  volume.  The  power  of  using  larger 
proportions  of  carbon  dioxide  was  doubtless 
acquired  in  an  earlier  geologic  period,  and  was 
adapted  to  the  conditions  then  prevalent. 

The  botanist  finds  himself  lost  in  a  maze  of 
conjecture  if  he  endeavors  to  trace  backward 
the  development  of  plants  and  determine  the 
''^^'^"^!l'°?  °^  point  at  which  they  gained  the  power  to  form 
chlorophyll.  It  is  quite  certain  that  the  simpler 
ancestral  forms,  which  consisted  of  simple 
masses  of  protoplasm,  were  not  able  to  con- 
struct and  maintain  a  substance  so  complex 
and  unstable  as  chlorophyll.  The  advent  of 
this  substance  into  the  living  world  marked 
the  attainment  of  a  comparatively  advanced 
stage  of  development.  A  tinge  of  probability 
lends  itself  to  the  theory  that  the  protoplasm 
of  all  simple  organisms  which  existed  in  a  far 
distant  age  of  the  world's  history  were  able 
to  accomplish  the  synthesis  of  complex  from 
simple  compounds,  and  that  the  "sulphur" 
and  "iron"  bacteria  are  but  remnants  of  this 
primitive  physiological  type. 

Still  another  problem  is  to  be  found  in  the 
presence  of  chlorophyll  in  a  number  of  the 
lower  forms  of  animals.  A  fact  which  renders 
the  task  of  making  categorical  distinction  be- 
tween plants  and  animals  still  more  difficult. 


LEAVES  IN  SEASONvS 


The  chlorophyll  is  not  found  in  the  organisms 
where  the  two  kingdoms  meet,  but  occurs  in 
animals  which  have  attained  a  high  degree 
of  development,  such  as  the  vorticella,  and 
fresh-water  sponges.  It  is  supposed  that  the 
chloroplasts  in  these  animals  are  descended 
from  others  derived  from  unicellular  plants 
captured  by  the  animals  in  an  earlier  stage 
of  the  development. 

To  a  naturalist  one  of  the  striking  and 
spectacular  features  in  the  history  of  living 
things  is  the  manner  in  which  vegetation  puts 
on,  wears,  and  discards  its  leafy  coverings  of 
green.  The  season  begins  with  the  assump- 
tion of  an  all  prevalent,  delicate  green  cover- 
ing, composed  of  millions  of  irregular  laminae  leaf-fail 
of  every  conceivable  form,  which  hide  the 
roughnesses  of  gnarled  and  crooked  branches, 
the  flinty  soil  and  ragged  moor.  With  the 
advancement  of  the  leaves  toward  maturity, 
the  earlier  and  more  delicate  tint  deepens  into 
a  rich  satisfying  green  that  fills  the  eye,  and 
then  fades  away  in  the  long  summer  heat  to 
dull  gray  and  bluish  greens,  dust-colored  and 
bearing  the  marks  of  many  subduing  strug- 
gles with  wind  and  storm.  The  first  breath 
of  frost  is  the  signal  for  a  change  on  slopes, 
valleys,  forests  and  meadows,  by  which  the 
dull  monotones  are  at  once  converted  into  a 


Autumnal 


154  LIVING  PLANTvS 

harmonious  magnificence  of  color,  as  if  by 
magic. 

The  splendor  of  the  colored  markings  of  the 
plants  and  animals  of  the  tropics  is  a  well 
worn  theme  with  amateurs,  but  it  does  not 
stand  comparison  with  the  beauty  of  the  au- 
tumnal tintsof  foliage  of  the  north  temperate 
zone,  either  in  variety  or  richness  of  tone. 
Furthermore  it  may  be  said  that  the  display 
offered  by  the  forests  east,  west  and  south  of 
the  Great  Lakes  in  North  America  is  not  du- 
plicated on  any  part  of  the  globe.  The  vege- 
tation of  the  valleys  and  mountain  slopes  of 
the  basins  of  the  Rhine  and  Danube  gives  an 
exhibit  which  is  only  less  beautiful  because  of 
the  smaller  number  of  species,  and  which  is 
less  remarked  because  of  its  shorter  duration. 

On  some  portions  of  the  earth's  surface 
within  the  tropics,  where  no  great  or  sharply 
defined  alterations  in  seasons  occur,  vegeta- 
tion pursues  a  fairly  even  course  all  the  year 
round .  Each  leaf  retains  its  place  on  the  stem 
until  the  full  limit  of  its  usefulness  or  endur- 
ance has  been  reached,  and  then  withered  and 
woody  it  falls  to  the  ground  in  company  with 
such  of  its  fellows  as  may  have  reached  a 
similar  stage  at  the  same  time.  Of  the  myr. 
iads  of  leaves  borne  by  any  tree,  not  so  many 
are  cast  at  one  time,  as  to  bare  the  branches 
or  make  any  apparent   diminution  of  their 


LEAVES  IN  SEASONS 


number,  and  many  plants  exhibit  flowers  and 
fruit  as  well  during  the  year.  Such  favorable 
conditions  for  growth  are  found  only  in  certain 
circumscribed  areas,  as  a  large  proportion  of 
the  earth's  surface  within  the  tropics  has  a 
supply  of  moisture  during  one  part  of  the 
year  wholly  insufficient  for  the  needs  of  grow- 
ing vegetation,  and  on  the  approach  of  this 
dry  season  the  plants  in  rich  regions  discard 
all  or  a  greater  part  of  their  leaf  surfaces. 
This  shedding  of  leaves  is  not  attended  by 
many  of  the  more  prominent  features  of  au- 
tumnal leaves,  however. 

A  portion  of  the  year  in  the  temperate  zone 
is  characterized  by  a  protracted  low  temper- 
ature which  is  unfavorable  to  even  the  simpler 
forms  of  activity  of  protoplasm,  and  renders 
the  presence  of  a  great  expanse  of  leaf  surface 
not  only  useless  but  dangerous  to  plants 
growing  in  those  zones,  and  provision  is  made 
for  the  economical  disposition  of  the  foliage. 

Plants  growing  in  regions  with  this  alter- 
nation of  seasons  have  modified  the  primitive 
rhythm  of  protoplasm  in  such  manner  that 
they  manifest  annual  periods  of  rest  and  ac- 
tivity. While  this  yearly  period  has  been  ac- 
quired in  somewhat  recent  time  perhaps,  yet 
it  is  most  firmly  fixed  in  the  constitution  of 
the  plant  as  may  be  demonstrated  if  an  at- 
tempt is  made  to  grow  a  deciduous  tree  or 


LIVING  PLANTS 


shrub  in  a  conservatory  after  removal  from 
its  native  forest. 

The  full  significance  and  real  causes  of  the 
phenomena  attendant  upon  the  fall  of  leaves 
in  autumn  may  only  be  comprehended,  when 
the  uses  subserved  by  the  leaf,  and  the  forms 
of  activity  carried  on  underneath  its  surfaces 
are  recalled. 
All  the  summer  long  the  green  surfaces  have 
Activity  been  lifted  to  the  sunlight  and  b\'  the  magic 

of  leaf  Q^  -^g    potent    touch   have  taken  in  carbon 

dioxide  from  the  air  and  combined  it  with 
water  in  such  manner  as  to  form  highly  plas- 
tic substances,  which  flowing  steadily  to  dis- 
tant portions  of  the  plant  have  by  the  subtle 
alchemy  of  protoplasm  become  converted  into 
wood,  fiber,  and  cork,  hard,  firm  and  light 
as  such  things  only  may  be. 

The  scene  of  activity  in  the  leaf  is  laid  in  the 
columnar  and  variously  distorted  cells  con- 
taining the  green  color  bodies  (chloroplasts) 
and  these  cells  are  rich  in  protoplasm,  albu- 
minoids and  sugar.  A  steady  stream  of  wa- 
ter is  sucked  up  by  the  minute  hairs  on 
the  rootlets,  and  containing  mineral  salts 
in  solution,  has  poured  upward  into  these  cells 
during  the  entire  season.  A  small  amount  of 
the  water  has  been  used  in  coiubination  with 
carbon  dioxide  in  forming  food,  but  b\' far  the 
greater    proportion    has     been    evaporated 


LfiAYES  IN  SEASONS 


through  the  membranous  walls  into  the  air- 
spaces, and  passes  outward  through  the 
breathing  pores  (stomata)  into  the  open  air 
in  the  form  of  vapor.  The  quantity  of  water 
poured  into  a  thirsty  sky  in  the  heat  of  a  mid- 
summer day  is  by  no  means  inconsiderable, 
even  in  smaller  plants,  and  in  a  full-grown 
poplar  tree  may  amount  to  a  barrel.  As  the 
water  enters  the  roots  it  contains  from  one- 
ten-thousandth  to  a  thousandth  part  of  its 
weight  of  potassium,  calcium,  and  magnesium 
salts  in  solution,  and  it  evaporates  into  the 
air  leaving  the  mineral  compounds  in  the 
plant.  The  minerals  serve  important  uses  in 
building  up  protoplasm,  and  facilitating  the 
diffusion  of  food  substances  from  one  part  of 
the  plant  to  another.  Eventually  a  large 
proportion  of  these  substances  accumulate  in 
layers  on  or  in  the  cell  wall,  or  as  crystals  in 
the  cell  cavity,  particularly  in  the  leaf,  in  such 
condition  as  to  be  of  but  little  use  to  the  or- 
ganism, and  it  would  be  benefited  by  being 
freed  from  this  superfluous  matter.  Besides 
the  inward  condition  of  the  leaf,  changes  in 
the  environmental  conditions  make  it  highly 
important  that  the  plant  should  dispense 
with  its  leafy  extensions. 

With  the  approach  of  the  close  of  the  grow- 
ing season,  the  outward  conditions  have  un- 
dergone a  gradual  and  thorough  change  and 


168  LIVING  PLANTvS 


the  tree  finds  its  enormous  leaf  surface  throw- 
ing water  into  the  surrounding  dry  atmo- 
sphere much  faster  than  it  may  be  taken  from 
the  soil  b}'  the  delicate  absorbing  organs. 

The  approach  of  autumn  brings  cool  nights 
and  a  consequent  great  radiation  of    heat 
Cause  of  from  the  soil.    The  chilled  root  hairs  in  the 

leaf-fall  g^jj  ^^^^  unable  to  take  the  necessary  supply 

of  water,  and  whenever  the  supply  of  moisture 
coursing  upward  through  the  sinuous  roots 
and  tall  stems  becomes  less  than  that  evapo- 
rated, adjustment  must  be  made  or  damage 
will  ensue.  The  plant  is  a  most  delicately 
self-regulating  organism.  It  cannot  increase 
the  water  supply ,  but  it  may  and  does  decrease 
the  evaporating  surface  by  casting  or  shed- 
ding the  leaves,  a  reaction  which  it  exhibits 
to  other  conditions  as  well.  Like  the  true 
seaman,  however,  the  plant  does  not  shorten 
sail  by  cutting  away  its  canvas,  but  by  a  de- 
liberate and  well-timed  series  of  processes, 
withdraws  all  of  the  substances  from  the  leat 
which  may  be  useful  to  it,  back  into  its  body 
before  it  discards  the  empty  sheets  of  cells  and 
woody  fibers  of  the  petiole  and  lamina. 

Before  proceeding  to  a  description  of  the 
mechanism  of  leaf-fall,  it  may  be  well  to  call 
attention  to  the  popular  and  erroneous  idea 
that  the  coloring  and  casting  of  autumnal 
leaves  is  due  to  the  action  of  frost.     It  is  true 


LEAVEvS  IN  SEAvSONS 


that  the  phenomena  of  autumnal  leaf-fall  are 
due  to  low  temperatures,  but  as  may  be  seen 
from  the  above,  the  defoliation  of  the  plant  is 
not  a  reaction  to  the  cold,  but  is  an  adjust- 
ment to  the  limited  water  supply  furnished  by 
the  chilled  roots.  The  reduction  of  the  water 
supply  and  the  beginning  of  the  processes 
leading  to  defoliation  occur  a  long  time  before 
the  temperature  of  the  air  is  depressed  to  the 
freezing  point,  or  the  formation  of  frost.  The 
influence  of  low  temperatures  upon  the  plant 
is  illustrated  by  the  manner  in  which  leaves  of 
tobacco  and  melon  plants  blacken  and  die  as 
the  result  of  cool  nights  before  the  occurrence 
of  frost.  These  plants  transpire  a  relatively 
large  amount  of  water  from  the  broad  leaves, 
and  if  the  temperature  of  the  soil  descends  to 
forty  degrees  Fahrenheit,  the  roots  are  unable 
to  take  up  the  necessary  supply  of  water,  and 
the  leaves  are  literally  dried  out,  though  the}-- 
are  incorrectly  described  as  frozen  or  frosted 
by  gardeners. 

The  casting  of  the  leaf  is  not  a  sudden  and  Withdrawal  of 
quick  response  to  any  single  depression  of  the  kaf-substance 
temperature,  but  is  brought  about  by  a 
complex  interplay  of  processes  begun  days  or 
perhaps  weeks  before  any  external  changes 
are  to  be  seen.  The  leaf  is  rich  in  two  classes 
of  substances,  one  of  which  is  of  no  further 
benefit  to  it,  and  another  which  it  has  con- 


LIVING  PLANTS 


structed  at  great  expense  of  energy,  and  which 
is  in  a  form  of  the  highest  possible  usefuhiess 
to  the  plant.  To  this  class  belong  the  com- 
pounds in  the  protoplasm,  the  green  color 
bodies,  and  whatever  surplus  food  may  not 
have  been  previously  conveyed  away.  The 
substances  which  the  plant  must  needs  dis- 
card are  in  the  form  of  nearly  insoluble  crys- 
tals, and,  by  remaining  in  position  in  the  leaf, 
drop  with  it  to  the  ground  and  pass  into 
that  great  complex  laboratory  of  the  soil 
where  by  slow  methods  of  disintegration,  use- 
ful elements  are  set  free  and  once  again  may 
be  taken  up  by  the  tree  and  travel  their 
devious  course  through  root  hairs  along  the 
sinuous  roots  and  up  through  million-celled 
columns  of  the  trunk  out  through  the  twigs 
to  the  leaves. 

The  plastic  substances  within  the  leaf  which 
would  be  a  loss  to  the  plant  if  thrown  away, 
undergo  quite  a  different  series  of  changes. 
These  substances  are  in  the  extremest  parts 
of  the  leaf,  and  to  pass  into  the  plant  body, 
must  penetrate  many  hundreds  of  membranes 
by  diffusion  into  the  long  conducting  cells 
around  the  ribs  or  nerves,  and  then  down 
into  the  twigs  and  stems.  The  successful  re- 
treat of  this  great  mass  of  valuable  matter  is 
not  a  simple  problem.  These  substances  con- 
tain nitrogen  as  a  part  of  their  compounds 


LEAVES  IN  vSEASONS 


and  as  a  consequence  are  very  readily  broken 
down  when  exposed  to  the  sunlight.  In  the 
living  normal  leaf  the  green  color  forms  a  most 
effectual  shield  from  the  effects  of  the  rays, 
but  when  the  retreat  is  begun,  one  of  the  first 
steps  results  in  the  disintegration  of  the  chlor- 
ophyll. This  would  allow  the  fierce  rays  of 
the  September  sun  to  strike  directly  through 
the  broad  expanses  of  the  leaf,  destroying  all  ^°^°*"  ^^  ^  P*"°" 
within,  were  not  other  means  provided  for  *^<^**"g  s"^^" 
protection.  In  the  first  place,  when  the 
chlorophyll  breaks  down,  cyanophyll  (blue- 
green)  is  formed,  anthocyan  (blue- red)  is 
constructed  by  the  protoplasm,  and  at  the 
same  time  the  yellow  lipochromes  present  in 
the  cells,  chiefly  xanthophyll,  become  visible 
and  take  a  share  in  protecting  the  plastic  sub- 
stances, which  absorb  the  sun's  rays  in  the 
same  manner  as  the  chlorophyll,  so  that  the 
leaf  exhibits  outwardly  a  gorgeous  panoply 
of  color  in  reds,  yellow,  and  bronzes  that 
makes  up  the  autumnal  display.  From  the 
wild  riot  of  tints  shown  by  a  clump  of  trees 
or  shrubs,  the  erroneous  impression  might  be 
gained  that  the  colors  are  accidental  in  their 
occurrence.  This  is  far  from  the  case,  however. 
The  key-note  of  color  in  any  species  is  con- 
stant, with  minor  and  local  variations.  The 
birches  are  a  golden  yellow,  oaks  vary  through 
yellow-orange  to  reddish  brown,  the  red  maple 


I.IVING  PLANTS 


a  dark  red,  the  tulip  tree  a  light  3^ellow,  haw- 
thorn and  poison  oak  become  violet,  while  the 
sumacs  and  vines  take  on  a  flaming  scarlet. 
These  colors  exhibit  some  variation  in  accord 
with  the  character  of  the  soil  on  which  the 
plants  stand. 

From  the  above  it  is  to  be  seen  that  the 
color  of  autumnal  leaves  is  a  screen  under 
cover  of  which  the  protoplasm  retreats  into 
the  main  stem,  carrying  with  it  such  other 
substances  as  may  be  of  use  to  the  plant. 
With  the  coming  of  spring  the  advance  of 
living  matter  in  the  form  of  leaves  and  shoots 
is  protected  in  the  same  manner  by  layers  of 
reddish  violet,  or  reddish  brown  coloring  mat- 
ter, which  disappears  on  the  appearance  of 
the  green  coloring  matter. 

It  is  of  special  interest  to  learn  in  this 
connection  that  leaves  which  are  covered  with 
a  dense  growth  of  silky,  woolly  or  branching 
hairs  do  not  usually  exhibit  any  marked  au- 
tumnal colors.  The  presence  of  the  screen  is 
unnecessary  in  such  instances  because  of  the 
protection  afforded  by  the  matted  or  felted 
hairs  on  the  surfaces. 

At  a  time  previous  to  the  beginning  of  the 
withdrawal  of  the  contents  of  the  leaf,  or  the 
formation  of  the  autumnal  colors,  prepara- 
tions had  been  steadily  in  progress  for  cutting 
away  the  leaf  when  the  proper  time  should 


LEAVES  IN  SEASONS 


arrive.    At  some  point  near  the  base  of  the 

leafstalk,  the  formation  of  a  layer  of  special 

tissue  had  begun  between  the  woody  cylinder 

in  the  center  and  the  thin  epidermis.    When 

the  time  for  the  casting  of  the  leaf  arrives 

this  special  tissue   grows    rapidly,    pushing 

apart  or  cutting  the  cells  which  have  held  the 

leaf  rigidly  in  position,  in  such  manner  that 

finally  the  leaf  stalk  consists  of  the  brittle 

cylinder  of  wood  surrounded  by  the  loosely     .  ^^^^  *°" 

adherent  cells  of  this  newly  formed  layer  of 

separation.   The  merest  touch  or  breath  of  air 

will  split  the  layer  of  separation,  break  the 

wood,  and  allow  the  leaf  to  fall  to  the  ground. 

After  the  layer  of  separation  has  been  formed, 

a  frost  or  freeze  would  help  to  break  away 

the  fragile  strand  holding  the  leaf  in  place, 

but  exercises  no  other  direct  influence  on  the 

process. 

Many  plants  make  provision  for  cutting 
away  the  leaf  at  more  than  one  point.  The 
vine  forms  two  layers  of  separation,  one  at 
the  base  of  the  leaf-stalk,  and  the  other  at  the 
upper  end  below  the  blade.  Layers  of  separa- 
tion are  formed  at  the  base  of  the  main  leaf- 
stalk and  at  the  base  of  the  separate  leaflets 
in  such  compound  leaves  as  those  of  the  Vir- 
ginia creeper,  horse  chestnut  and  Ailanthus. 

It  is  to  be  remembered,  of  course,  that  all 
plants  do  not  discard  their  leaves  on  the  ap- 


LIVING  PI.ANTvS 


proach  of  the  inclement  season.     The  leaves 
of  evergreens  are  so  organized  that  they  may 
Evergreen  withstand  the  periods  of  drought  or  frost 

leaves  through  several  years.      Before  such   leaves 

enter  upon  a  period  of  inactivity,  alterations 
are  carried  on  in  the  cells,  among  which  are 
the  reduction  of  the  ]3roportion  of  water  pres- 
ent, and  chemical  changes  which  result  in  the 
formation  of  substances  not  affected  by  low 
temperatures.  The  changes  of  color  are  not 
so  marked  as  to  attract  general  attention, 
and  the^^  are  brought  about  by  the  withdrawal 
of  the  chlorophyll  bodies  toward  the  inner 
ends  of  the  cells,  and  the  formation  of  small 
proportions  of  yellow^ish  or  reddish  coloring 
substances.  The  retention  of  the  foliage  is 
made  possible  by  adaptations  in  form  and 
structure,  and  is  a  result  of  the  morphologi- 
cal nature  of  the  plants  involved. 


THE  SIGNIFICANCE  OF  COLOR.* 

The  colors  exhibited  by  the  roots,  stems, 
leaves  and  flowers  of  plants  must  have  been 
used  by  man  as  distinguishing  marks  in  the 
selection  of  food  at  quite  an  early  stage  in  his 
development.  Doubtless  masses  and  combi- 
nations of  the  cruder  colors  afforded  gratifi- 
cation to  his  dawning  sense  of  the  beautiful 
in  these  earlier  times.  Later  he  became  im- 
bued with  the  idea  that  man  was  the  center  Early  views 
of  the  universe  and  that  everything,  plants 
included,  was  meant  to  bear  a  good  or  evil 
relation  to  the  human  race.  In  the  deter- 
mination of  the  aspect  of  any  plant,  color 
and  form  were  taken  into  account,  and  were 
held  to  be  indicative  of  magical  curative  or 
poisonous  properties. 

*  Adapted  from  "The  Physiology  of  Color  in  Plants,"  Pop- 
ulnr  Science  Monthly,  Mav,  1S96. 


LIVING  PLANTS 


The  last-named  aspect  of  plant  colors  re- 
ceived its  greatest  attention  during  the  prev- 
alence of  the  practices  of  the  Grecian  Rhizo- 
tomoi  and  Pharmakopoli,  and  later  in  the 
"doctrine  of  signatures."  The  doctrine  of 
signatures  supposed  that  the  color  and  form 
of  plants  indicated  their  relations,  good  or 
evil,  to  the  human  race,  in  reference  to  v^hich 
they  were  especiall^v  created.  This  crude  su- 
perstition attained  greatest  favor  in  the  six- 
teenth century,  and  is  still  prevalent  in  obscure 
form  among  the  lower  classes  in  certain  por- 
tions of  Europe.  The  use  of  colors  as  a  dis- 
tinguishing mark  between  species,  families, 
and  groups  began  quite  early  in  the  history 
of  attempts  at  classification,  and  still  forms 
a  minor  character  in  modern  systems. 

A  consideration  of  the  plant  as  an  independ- 
ent organism,  and  of  colors  with  respect  to 
Sprengel's  the  possible  uses  to  the  species  forming  them 

discoveries  ^^^^^  ^^^^  given  by  Konrad  Sprengel  near  the 

close  of  the  eighteenth  centur}'.  In  his  won- 
derful hook,  Dns Entdeckte Geheimniss  clerNa- 
tur  im  Bail  unci  der  Befruchtiwg  der  Blumen, 
published  in  1793,  he  brought  out  the  view 
that  the  colors  of  flowers  are  for  the  pur- 
pose of  attracting  animals  which  would 
carry  pollen  from  one  individual  to  another. 
The  facts  involved  interest  many  classes  of 
naturalists,  and  observations  have  been  ex- 


considerations 


tended  in  every  direction  by  trained  and  un- 
trained workers  until  the  aggregate  mass  of 
results  is  nothing  short  of  colossal.  The  con- 
clusions advanced  by  Sprengel  have  been  ex- 
tended until  effort  has  been  made  to  show, 
that  not  only  does  the  plant  use  color  to  at- 
tract useful  insects  to  flowers,  but  that  it  also 
displays  luring  areas  of  color  and  stores  of 
nectar  on  distant  bracts  and  stems  to  lead 
unwelcome  and  harmful  visitors  away  from  Ecological 
the  neighborhood  of  the  reproductive  mem- 
bers. Still  further,  many  plants  are  supposed 
to  exhibit  colors  in  mimicry  of  some  danger- 
ous animal,  or  which  would  serve  as  a  signal 
of  warning  to  the  ravaging  animal  of  the 
presence  of  weapons  or  chemicals  hurtful  to 
it.  In  the  highly  speculative  consideration 
given  the  subject  the  general  principal  has 
been  drawn  upon  to  furnish  solutions  to  com- 
plicated or  unusual  arrangements  of  color,  in 
a  manner  highly  improbable  and  unscientific, 
and  in  many  instances  verging  upon  the  im- 
possible and  ridiculous.  That  it  can  not  be 
assumed  a  priori  that  the  colors  exhibited  by 
the  flowers  or  any  other  organ  of  the  plant 
are  devices  to  attract  and  guide  or  repel  ani- 
mal visitors  is  becoming  more  and  more  ap- 
parent. 

Recent  researches  have  demonstrated  that 
a  color  sense  is  almost  wholly  lacking  except 


LIVING  PLANTvS 


among  the  higher  insects,  and  that  the  form 
and  odor  of  the  flower  are  the  features  most 
effective  in  securing  the  attention  of  pollen- 
carrying  animals. 

It  is  of  course  undeniably  proven  that  some 
colors  do  attract  insects  to  flowers,  and  that 
pollination  is  accomplished  as  a  result  of  the 
visit.  If,  how^ever,  the  color  is  supposed  to  be 
developed  as  an  adaptation,  guided  by  the 
selective  agency  of  the  animal,  some  difficulties 
arise.  In  the  first  place,  it  is  to  be  said  that 
the  selective  power  of  the  insect  has  been  ex- 
ercised only  in  comparatively  recent  times — 
since  it  developed  the  sense  of  color.  Secondly 
the  red,  yellow,  and  white  floral  markings 
of  leaves  and  flowers,  as  well  as  of  other  mem- 
bers, are  due  to  katabolic  or  breaking  down 
processes,  and  originate  as  well  in  injured  or 
deteriorated  organs  in  which  the  food-forming 
capacity  has  suffered  diminution.  In  some 
instances,  as  in  the  screen  of  colored  leaves, 
the  formation  of  the  pigments  is  due  to  the 
regulatory  action  of  the  plant,  and  serves  the 
purpose  of  checking  the  diminution  of  the 
food-forming  power,  and  hinders  the  disin- 
tegration of  plastic  substances,  to  which  it 
owes  its  origin. 

With  all  of  the  probabilities  taken  into  ac- 
count it  can  only  be  said  that  the  selective 
power  of  animals  toward  plant  colors  may 


have  accentuated  the  development  of  these 
substances  in  certain  directions  in  lines  deter- 
mined by  inherent  physiological  properties, 
the  origin  as  well  as  the  continuation  of 
which  are  entirely  independent  of  the  prefer- 
ences of  the  animal.  If  insects  and  birds  do, 
in  certain  instances,  show  a  preference  for  any 
color  or  color  scheme  it  merely  converts  an 
indifferent  to  a  useful  property.  This  is  true 
of  attractive  as  well  as  of  warningcolors.  By 
a  recent  series  of  experiments  with  a  number 
of  !tropical  plants  w^iich  have  a  color  scheme 
resembling  that  of  a  poisonous  snake,  which 
has  been  supposed  to  shield  them  from  attack 
by  animals,  it  has  been  found  that  the  degree 
of  hunger  of  the  animals — snails,  rabbits,  an- 
telopes, etc.— chiefly  determines  the  choice  of 
food,  and  that  warning  devices  serve  no  ac- 
tual use  so  far  as  has  been  actually  demon- 
stra'^ed. 

It  will  be  found  most  convenient  to  discuss 
the  chemical  nature  and  physiological  uses  of 
the  more  prominent  coloring  substances,  under 
the  heads  of  chlorophyll,  etiolin,  lipochromes,  Enumeration 
anthocyan  or  erythrophyll,  and  various  spec- 
ial colors  both  red  and  yellow,  to  be  found 
within  the  limits  of  families,  or  ecological 
groups.  The  manner  of  occurrence  and  their 
universal    unstability    are    such  that  it  has 


of  colors 


LIVING  PLANTS 


Chlorophyll 


been  impossible  to  determine  their  exact  chem- 
ical composition. 

Chloroph3^]l  is  perhaps  the  most  important 
coloring  substance  in  the  world,  for  upon  this 
substance  depends  the  characteristic  activity 
of  plants,  the  synthesis  of  complex  compounds 
from  carbon  dioxide  and  water — a  process 
upon  which  the  existence  of  all  living  things 
is  ultimately  conditioned.  Only  in  a  very  few 
unimportant  forms  devoid  of  chlorophyll  can 
the  synthesis  of  complex  from  simple  com- 
pounds, or  from  the  elements,  be  accomplished. 
The  function  of  chlorophyll  may  only  be  com- 
prehended when  its  chief  physical  properties 
are  understood.  These  may  be  best  illustrated 
if  a  solution  of  the  substance  is  obtained  by 
placing  a  gram  of  chopped  leaves  of  grass 
or  geranium  in  a  few  cubic  centimeters  of 
strong  alcohol  for  an  hour.  Such  a  solution 
will  be  of  a  bright,  clear  green  color,  and 
when  the  vessel  containing  it  is  held  in  such  a 
manner  that  the  sunlight  is  reflected  from  the 
surface  of  the  hquid  it  will  appear  blood-red, 
due  to  its  property  of  fluorescence,  that  of 
changing  the  wave  length  of  the  ra^'s  of  light 
of  the  violet  end  of  the  spectrum  in  such 
manner  as  to  make  them  coincide  with  those 
of  the  red  end.  It  is  by  examination  of  light 
which  has  passed  through  a  solution  of  chloro- 
phyll, however,  that  the  greatest  insight  into 


Red         Yellow        Green    Blue     Indigo      Violet 

Fir..  17.— Curves  Showing  Synthetic,  Thermal  and  Disinteorat- 

iNG  Effects  of  the  Regions  of  the  Solar 

Spectrum.      After  Pfeffer. 

Svntbesis.  Heat.     —  ■ Disintegration. 


Fig.  18.— I.  Spectru.m  of  Chlorophyll  with  Seven  Ab- 
sorption Bands.  The  two  in  the  red-yellow  between  B  and  D, 
and  the  three  in  the  bhie-violet,  beyond  F,  blended  in  the  dia- 
gram, are  the  most  important  and  characteristic. 

II.  Spectrum  of  Amaranth-rkd.  All  the  rays  except  those 
falling  between  B  and  D  have  been  absorbed. 

III.  Spectrum  of  Autumnal  Color  of  Leaves  of  Ampelop- 
sis.  All  the  rays  except  a  part  of  those  falling  between  C  and  D 
have  been  absorbed. 


LIVING   PLANTS 


its  physical  properties  may  be  gained.  If 
such  a  ray  of  light  is  passed  through  a  prism 
and  spread  out  on  a  screen,  it  may  be  seen 
that  there  are  several  large  intervals  or  dark 
bands  in  the  spectrum.  The  rays  of  light 
which  would  have  occupied  these  spaces  have 
been  absorbed  by  the  chlorophyll,  and  con- 
verted into  heat  and  other  forms  of  energy. 
This  energy  is  directly  available  to  the  proto- 
plasm containing  the  chlorophyll,  and  by 
means  of  it  the  synthesis  of  complex  substances 
may  be  accomplished.  Moreover,  the  amount 
of  synthesis  accomplished  by  plants  exposed 
to  separate  portions  of  the  spectrum  will  be 
directly  proportional  to  the  amount  of  that 
portion  which  can  be  absorbed  and  converted 
into  useful  forms  of  energy.  The  amount  of 
synthesis  is  shown  to  be  greatest  in  the  red 
rays  between  B  and  C,  where  the  most  com- 
plete absorption  takes  place. 

Chlorophyll  is  a  very  complex  and  highly 
unstable  substance,  and  during  the  absorp- 
tion of  light  it  is  slowW  broken  down,  but  or- 
dinarily it  is  rebuilt  by  the  protoplasm  as 
fast  as  it  is  decomposed.  If,  however,  the 
chlorophyll  and  the  leaf  containing  it  are  ex- 
posed to  a  light  of  such  intensity  that  the 
chlorophyll  is  decomposed  faster  than  it  can 
be  rebuilt,  then  damage  must  ensue,  wliich  if 
sufficientlv  extensive  will   result  in  the  death 


of  the  entire  leaf.  The  intensity  of  the  light 
which  induces  a  maximum  of  activity  in  any 
plant,  and  which  it  may  receive  without  dam- 
age, is  determined  by  its  specific  constitution. 


Fig.  19. — Transyekse  Sections  through  the  Frond  of 
Lemna  trisulca  (Duckweed),  Showing  Different  Posi- 
tions OF  Chlorophyli,  Bodies.  A,  position  in  diflfuse  light ; 
B,  in  strong  light  striking  the  surface  perpendicularly ;  C,  in 
darkness.     After  Stahl. 

In  the  greater  majority  of  plants  the  efficien- 
cy of  the  chlorophyll  increases  in  tempera- 
tures up  to  35°  centigrade,  varies  from  35  to 


LIVING  PI.ANTvS 


40C,  and  steadily  decreases  from  40  to  50°C. 
where  activity  wholly  ceases.  The  intensity 
of  light  falling  on  a  plant  in  an  open  plain 
during  twenty -four  hours  ranges  from  almost 
total  darkness  to  the  blaze  of  the  noonday 
sun,  and  varies  almost  momentarily.  As  an 
adjustment  to  this  condition  the  intensity  of 
the  light  impinging  on  the  chlorophyll-bearing 
masses  of  protoplasm  is  varied  by  altering  the 
position  of  the  surfaces  of  the  leaves  by  active 
and  passive  movements.  In  others  in  which 
this  movement  is  not  possible— such,  for  ex- 
ample, as  the  leaflike  duckweeds  which  float 
on  the  surface  of  the  water — the  intensity  of 
the  light  received  is  regulated  by  alterations 
in  the  position  and  distance  of  the  chlorophyll 
from  the  surface  of  the  organ. 

In  many  plants  growing  in  the  bright  glare 
of  the  sun  a  thickened  cuticle  or  a  heavy  coat 
of  hairs  serves  to  protect  the  chlorophyll 
against  the  more  intense  action  of  the  rays. 
Then,  as  will  be  shown  later,  other  colors  are 
often  developed  in  the  external  layers  of  the 
leaf  as  a  protection  against  intense  illumina- 
tion. 

Chlorophyll  is  generally  formed  in  special 
sponge-like  masses  of  protoplasm  (  chloro- 
plasts)  in  the  peripheral  layers  in  the  cell,  and 
is  most  abundant  in  leaves. 

As  a  rule  the  chloroplasts  may  form  chloro- 


phyll  only  in  sunlight,  though  several  instan- 
ces are  known  in  which  the  green  color  is  to 
be  found  in  tissues  in  complete  darkness.  The 
presence  of  iron  in  the  cell  is  necessary  for  the 
formation  of  chlorophyll,  although  it  does 
not  enter  into  the  composition  of  the  pigment. 

When  a  plant  is  grown  in  complete  darkness 
it  assumes  a  pale  waxy  yellow  color,  the  or- 
gans are  usually  abnormal  in  size  and  form, 
and  are  said  tohc etiolated.  The  yellow  color 
of  etiolated  plants  is  etiolin  which  resembles  Etioli 
chk»rophyll  in  general  chemical  composition 
and  ph3'sical  properties.  Many  writers  be- 
lieve that  etiolin  is  formed  in  the  earlier  stages 
of  the  construction  of  the  chlorophyll  mole- 
cules. In  support  of  this  view  it  has  been  no- 
ticed that  plants  grown  in  darkness  and  con- 
taining large  quantities  of  etiolin  turn  green 
on  exposure  to  light  much  more  rapidly  than 
those  in  which  but  little  etiolin  was  found. 
Etiolin  is  not  to  be  confused  with  the  yellow 
colors  of  fruits  and  flowers,  which  are  due  to 
an  entirely  different  class  of  pigments  next  to 
be  considered. 

The  lipochromes  are  a  series  of  substances 
varying  through  yellow  and  red,  devoid  of 
nitrogen,  and  which  absorb  certain  blue  violet  ^ul^T 
rays  of  sunlight.  These  substances  occur  in 
company  with  chlorophyll  in  leaves  and  else- 
where in  bacteria,  algse,  fungi,  as  well  as  in 


chromes 


LIVING  PLANTS 


the  flowers  and  fruits  of  the  seedforming 
plants.  The  lipochromes  constitute  the  pig- 
ments of  many  animals  also.  Examples  in 
the  two  groups  are  offered  by  the  yellow  color 
of  the  yolk  of  a  hen's  egg,  and  by  the  reddish 
yellow  of  the  carrot,  or  the  sulphur  yellows 
of  certain  fungi.  These  substances  occur  in 
various  forms,  in  oily  drops  in  the  fungi,  in  a 
diffused  state  throughout  the  plasma  in  bac- 
teria, and  in  crystalloids  in  the  carrot  and  in 
flowers.  In  leaves  the  lipochromes  are  sup- 
posed to  occur  in  the  chloroplasts.  If  an 
equal  amount  of  kerosene  or  benzole  is  added 
to  a  solution  of  chlorophyll  in  alcohol  and  the 
mixture  is  shaken  and  allowed  to  stand  for  a 
few  hours,  the  alcohol  containing  a  yellowish 
lipochrome,  xanthophyll,  wnll  separate  from 
the  kerosene  or  benzole  solution.  The  yel- 
low and  yellow-red  tints  of  au  tumn  leaves  are 
due  to  the  lipochromes  which  become  visible 
after  the  decomposition  of  the  chlorophyll. 

In  leaves  the  lipochromes  are  supposed  to 
act  as  a  screen  in  preventing  the  disintegrat- 
ing action  of  light  on  nitrogenous  substances. 
Since  the  lipochromes  disappear  during  the 
germination  of  the  spores  of  fungi  it  is  sug- 
gested that  a  function  as  reserve  substance  is 
also  subserved.  Colored  bacteria  in  which  the 
pigment  is  a  lipochrome  of  which,  Bacillus 
brunneus,  B.  cinnhareus,   Micrococcus  agilis 


and  Sarcina  rosea  offer  examples,  have  the 
power  of  occluding  oxygen  from  the  air, which 
may  be  given  off  under  partial  pressure.  The 
pigment  is  the  oxygen  carrier  and  may  act  in 
a  similar  manner  after  it  has  been  extracted 
from  the  organism.  The  green  and  purple 
bacteria  of  which  Bacterium  viride  and  B.pho- 
tometricum  are  examples,  contain  two  pig- 
ments one  of  which  resembles  chlorophyll  and 
the  other  the  red  coloring  matter  of  the  algge. 

The  anthocyans  comprise  a  series  of  sub- 
stances soluble  in  water  varying  from  red  to 
blue  and  violet  according  to  the  acid  or  alka- 
line nature  of  the  cell  sap  in  which  they  are 
always  found  in  solution.  Thus  a  portion  of  Anthocyans 
a  plant  of  a  blue  color  from  the  presence  of 
anthocyan  may  be  changed  to  a  red  by  im- 
mersion in  an  acid  solution  and  the  operation 
may  be  reversed.  Similar  changes  are  often 
brought  about  in  the  petals  of  flowers  by 
chemical  processes  set  up  within  the  cell.  Ex- 
amples of  changes  of  this  character  are  shown 
by  Pulmonaria,  Mertensia,  Symphytum  and 
willows. 

The  anthocyans  occur  in  stems,  petioles, 
flowers,  leaves,  unfolding  shoots,  organs  ex- 
posed to  low  temperatures,  and  in  injured 
regions.  It  is  quite  generally  accepted  that 
the  pigments  embraced  in  this  group  are  de- 


LIVING  PLANTvS 


rived  from   the  tannins.     The  colors  which 
attract  animals  belong  chiefly  to  this  group. 

Several  theories  have  been  proposed  in  the 
last  decade  to  account  for  the  functions  of 
Relation  of  an-  anthocyan.  Engelmann  found  that  red  pig- 
thocyan  to  light  j^^g^^  permits  90  per  cent  of  the  orange  rays, 
10  to  30  per  cent  of  the  green  and  yellow,  50 
per  cent  of  the  blue  and  80  per  cent  of  the 
violet  to  be  transmitted  unchanged.  Miiller 
has  jDlotted  the  absorption  spectrum  of  a  large 
number  of  anthocyans,  with  the  result  that 
while  Engelmann's  results  hold  good  in  the 
main,  some  also  absorb  the  lower  red  rays. 
As  a  natural  result  of  such  physical  character- 
istics it  is  found  that  anthocyan  converts 
lightintoheat,  a  portion  of  the  converted  light 
being  the  disintegratingraysof  theblue  violet 
end  of  the  spectrum.  That  the  anthocyan  does 
partially  retard  the  disintegration  of  chlor- 
ophyll by  hght  may  be  seen  if  two  vessels  con- 
taining solutions  of  chlorophyll  are  so  ar- 
ranged that  the  light  which  strikes  on  one  of 
them  shall  first  pass  through  a  parallel- walled 
vessel  containing  water,  and  that  which 
strikes  the  other  through  a  similar  vessel  con- 
taining a  solution  of  anthocyan.  The  chlor- 
ophyll in  the  first  will  soon  become  much  more 
^  discolored  than  in  the  second,  which  has  re- 

ceived light  transmitted  through  anthocyan. 
That  the  disintegrating  rays  may  be  convert- 


COLOR  179 

ed  into  heat  is  demonstrated  by  the  following 
ingenious  experiment  designed  by  Kny. 
Three  similar  glass  vessels  with  parallel  walls 
are  filled  with  distilled  water.  In  one  vessel 
a  number  of  green  leaves  of  canna  are  placed, 
and  in  another  such  number  as  to  offer  the 
same  amount  of  surface  as  those  in  the  first, 
but  which  contain  a  large  amount  of  antho- 
cyan.  The  third  vessel  is  left  unchanged,  and 
all  are  placed  in  sunlight  of  equal  intensity. 
A  certain  rise  in  temperature  naturally  ensues 
in  the  water  in  the  third  vessel ;  a  greater  rise 
occurs  in  the  first,  showing  that  chlorophyll 
converts  a  portion  of  the  light  into  heat, 
while  the  greatest  increase  takes  place  in  the 
second,  where,  in  addition  to  the  action  of 
the  chlorophyll,  the  converting  power  of  the 
anthocyan  is  exerted.  The  difference  between 
the  temperature  of  the  vessels  containing  the 
green  and  red  leaves  often  amounts  to  4°  C, 
which  is  due  entirely  to  the  action  of  the 
anthocyan. 

The  "screen  theory"  supposes  that  the  chief 
purpose  of  anthocyan  is  to  protect  chlorophyll  ^j^ 
and  other  nitrogenous  and  unstable  sub-  theory 
stances  in  transit  and  in  situ  from  being 
broken  down  by  the  too  intense  action  of 
light  ra3^s,  A.  second  theory  holds  that  the 
development  of  heat  and  energy  from  a  layer 
of  anthocvan  is  an  aid  to  the  translocation 


screen 


LIVING  PLANTS 


of  carbohydrates  and  other  substances  from 
one  part  of  the  plant  to  another,  notably 
starch, from  theleaves  to  the  stem.  The  third 
theory  consists  of  the  idea  that  the  heat  de- 
veloped by  anthocyan  serves  chiefly  as  an  aid 
in  promoting  transpiration.  Many  facts  are 
at  hand  supporting  both  the  first  and  last 
named  speculations,  though  the  argument  in 
either  case  has  not  advanced  to  the  stage  of 
absolute  proof.  As  for  the  second,  many 
plants  growing  in  cold  situations  are  un- 
doubtedly able  to  carry  on  metabolism  to  bet- 
ter advantage  because  of  the  heat  derived 
from  light  by  layers  of  anthocyan  present. 

The  "screen"  theor^^  receives  support  from 
the  fact  that  the  upper  layers  of  leaves  of 
plants  growing  in  intense  sunlight  and  in  ex- 
posed Alpine  situations  are  furnished  with 
laj'ers  of  color  on  the  upper  or  illuminated 
surfaces  of  the  leaves,  as  are  also  the  leaves 
of  many  shade-loving  plants  when  grown  in 
free  sunlight.  It  is  likewise  asserted  that 
plants  devoid  of  color  growing  in  the  low- 
lands will  develop  anthoc3'an  in  the  leaves 
w^hen  transplanted  to  Alpine  elevations.  Ker- 
ner  transplanted  the  summer  savory  (Satur- 
eja  hortensis)  from  lowland  to  a  height  of 
3,200  meters  and  found  that  it  developed  a 
very  strong  layer  of  anthocyan.  Ewart  foiuid 
that  the  plants  on  the  summit  of  the  moun- 


tain  Geddeh,  4500-6500  feet,  in  Java,  with 
a  very  moist  air  have  but  little  anthocyan 
while  on  Pangerango,  at  a  height  of  10,000 
feet,  with  a  dry  atmosphere  the  presence  of  red 
coloring  matter  was  ver^-  marked.  The  pow- 
er of  absorbing  the  photochemical  rays  pos- 
sesvsed  by  moist  air  would  preclude  the  need 
of  a  protective  coloring  in  the  first  instance. 
The  writer  has  noticed  that  the  young  and 
pendant  leaves  of  the  mango  (Mangifera)  are 
but  slightly'  colored  in  the  lowland  habitats 
of  the  tree  in  Jamaica  but  on  the  mountain 
sides,  near  1000  feet,  the  young  bunches  show 
a  perfect  blaze  of  color  especially  in  dry  reg- 
ions. Here,  as  in  the  highly  colored  young 
leaves  of  the  maple,  oak,  grape,  sumac,  alder 
and  others,  the  red  coloring  matter  douljtless 
serves  as  a  protection  against  the  penetrating 
rays  of  the  sun.  At  the  same  time  it  is  to  be 
borne  in  mind  that  the  low  temperatures  of 
the  elevations  mentioned,  or  of  the  spring 
season  may  be  the  direct  cause  of  the  forma- 
tion of  the  anthocyan. 

The  most  satisfactory  proofs  of  the  forma- 
tion of  anthocyan  as  a  screen  are  given  by  the 
exposure  to  daylight  of  plants  growing  in 
darkness.  Under  such  circumstances  the 
pearly  white  rhizomes  of  Dentaria  hulbifera 
become  violet.  Plants  of  Philotria  canaden- 
sis (Elodea)  and  Utricularia  vulgaris  grown 


LIVING  PI-ANTS 


in  weak  sugar  solutions  in  strong  light 
formed  anthocyan,  while  other  specimens  in 
water  and  exposed  to  diffuse  light  did  not, 
showing  that  the  color  is  formed  when  needed 
only,  and  not  accidentally,  although  its  oc- 
currence as  in  underground  organs  or  in  the 
center  of  massive  tissues  must  be  accidental 
and  not  useful. 

Anthocyan  as  a  screen  is  not  always  con- 
fined to  the  upper  layers  of  the  leaf.  The 
leaves  of  the  banana  (Musa)  are  vertical  and 
rolled  up  with  the  ventral  surfaces  outermost 
when  young.  One  species  develops  color  on 
the  under  side,  which  disappears  as  the  leaf 
unrolls  and  comes  down  to  a  horizontal  posi- 
tion. Uncaria,  Alpina,  Belemcanda,  and  other 
plants  afford  similar  instances.  The  pinnules 
of  Alimosa  pudica  are  provided  with  a  red- 
dish coloring  matter  in  the  surfaces  of  the 
lower  sides  whicii  are  exposed  when  closed 
together  in  the  "hot  sun"  position. 

The  coloring  matter  in  the  pistils  of  anemo- 
philous  plants  such  as  Populus,  Salix,  Plata- 
nus,  Ulmus,  Ostrya,Carpinus,  Corylus,  Alnus, 
Acer,  Fraxinus,  Rumex,  and  others  in  which 
it  can  have  no  possible  significance  for  animals, 
also  serves  as  a  screen  against  the  effects  of 
light.  The  growth  of  the  pollen  tube  down 
through  the  pistil  would  be  very  much  hindered 


by  the  action  of  light,  which  is  prevented  by 
the  screening  anthocyan. 

The  demonstrations  of  the  useful  properties 
of  anthocyan  as  a  developer  of  heat  for  pro- 
moting the  chemical  processes  are  not  nearly 
so  numerous.  The  opening  of  the  flowers 
of  some  of  the  alpine  grasses  is  brought  about 
by  the  ra])id  elongation  of  the  colored  anthers 
under  the  influence  of  sunlight.  It  is  suggested 
that  the  energy  for  the  rapid  growth  is  de- 
rived from  the  sunlight  by  the  coloring  mat- 
ter. It  is  quite  true  that  the  heat  from  any 
source  will  cause  these  flowers  to  open  quickly. 
The  red  color  of  certain  gymnospermous  flow- 
ers may  accelerate  their  opening  in  the  same 
manner. 

The  presence  of  layers  of  color  in  the  lower 
sides  of  rosettes,  and  in  leaves  and  rapidly 
growing  organs  in  the  deep  recesses  of  jungles 
and  swamps,  admits  of  no  interpretation  ex- 
cept that  such  arrangements  are  useful  in 
promoting  transpiration  by  means  of  the 
heat  developed.  If  a  red  and  green  leaf  of  the 
same  species  are  placed  with  their  bases  in 
sunlight  with  the  bases  of  the  petioles  placed 
in  calibrated  cylinders  full  of  water  it  will  be 
found  that  the  transpiration  is  most  rapid 
from  the  colored  leaf  since  it  absorbs  the 
greatest  amount  of  water.  A  very  obvious 
demonstration  may  also  be  made  if  the  base 


Promotion  of 
metabolism 


Promotion  of 
transpiration 


184  LIVING  PLANTS 

of  the  petiole  of  a  leaf  containing  patches  or 
spots  of  color  is  placed  in  an  aniline  solution. 
The  d\'e  will  pass  most  quickly  and  rapidly  to 
the  regions  containing  anthocyan,  indicating 
that  the  loss  of  water  has  been  greatest  from 
these  areas. 

The  maintenance  of  a  transpiration  stream, 
laden  with  mineral  salts,  to  leaves  and  rapid- 
ly growing  shoots  in  an  already  moist  and 
warm  atmosphere  is  a  matter  of  some  diffi- 
culty and  importance.  If  the  temperature  of 
a  plant  is  higher  than  the  surrounding  atmo- 
sphere it  may  continue  to  carry  on  transpira- 
tion because  of  the  greater  tension  of  the 
aqueous  vapor  in  the  heated  air  of  the  inter- 
cellular spaces  than  in  the  surrounding  med- 
ium. The  presence  of  anthocyan  would  be 
almost  a  necessity  to  leaves  under  such  cir- 
cumstances. 

In  connection  with  the  heat  producing  prop- 
erties of  anthocyan  it  is  to  be  said  that  it  may 
increase  the  amount  of  odorous  substances 
volatilized  from  fragrant  flowers,  and  thus  in- 
directly aid  pollination.  It  is  also  possible 
that  the  actual  warmth  of  organs  containing 
anthoc3'an  may  serve  as  a  lure  to  animals. 

A  number  of  pigments  of  limited  distribu- 
tion occur  in  the  citrus  fruits,  colored  alg?E 
and  bacteria,  which  are  but  little  known  so 


Red  sea-weeds 


far  as  composition  and  use  are  taken  into  ac- 
count. 

The  color  of  the  red  seaweed  is  due  to  the 
presence  of  phyco-erythrophyll  which  is  pres- 
ent in  the  protoplasm  associated  with  chloro- 
phyll. It  is  to  be  noted  here  that  the  antho- 
cyansare  dissolved  in  the  cell  sap  of  the  plants 
in  which  they  occur.  The  gradation  of  the 
amount  of  phyco-erythrophyll  at  different 
depths  suggests  that  the  color  serves  the  pur- 
pose of  converting  light  into  heat  useful  in 
promoting  metabolism.  The  presence  of  a 
red  pigment  in  Haematococcusand  the  resting 
spores  of  many  algae  is  doubtless  a  protection 
against  the  disintegrating  effect  of  light  on 
chlorophyll  and  protoplasm. 

Effects  quite  as  marked  as  those  produced 
133^  colors  may  be  brought  about  by  the  pres- 
ence or  mechanical  arrangement  of  certain  Markings  not 
cells.  The  shade  of  green  presented  by  a  leaf  '^"^  *°  '^°'°*' 
will  be  determined  by  the  number  and  posi- 
tion of  the  chlorophyll  bodies  with  respect  to 
the  surface.  Coatings  of  wax,  min-^ral  salts, 
and  hairs  also,  bring  about  modifications. 
The  silvery  or  silver  gray  or  whitish  appear- 
ance of  surfaces  is  due  to  the  loose  arrange- 
ment of  the  sub-epidermal  cells  forming  great 
intercellular  spaces,  The  multifold  refractions 
offered  by  the  numerous  free  walls  of  the  cells 
prevents  the  penetration  of  the  leaf  by  light. 


LIVING  PLANTS 


Fig.  20. — 1.  Transverse  section  of  a  velvety  leaf  of  Eran- 
themtim  Cooperi.  The  epidermal  cells  of  the  "upper  side  are 
furnished  with  elongated  papillose  extensions  for  entrapping 
sunlight.  The  extremities  of  some  cells  are  converted  into 
hairs.     The  epidermis  of  the  lower  side  contains  anthocyan. 

2.  Diagram  showing  the  manner  in  which  light  enters  the 
epidermal  cells  of  velvety  surfaces. 


The  tissues  underneath  such  regions  are  usu- 
ally free  from  chlorophyll.  The  leaf  might  be 
compared  to  a  sheet  of  tinted  glass  which  per- 
mits the  passage  of  the  greater  part  of  the  light 
which  falls  upon  it  while  intact.  When 
crushed  into  fragments  the  mass  of  minute 
fragments  reflects  back  the  rays  at  thousands 
of  points. 

Plants  such  as  the  aloe,  growing  in  the 
fierce  light  of  a  tropical  desert,  avoid  burning 
and  dr3ang  of  the  tissues  by  such  arrange- 
ments. The  silvery  areas  w^arm  up  much 
more  slowly  than  a  typical  leaf.  At  the  same 
time  this  feature  is  also  of  use  to  plants  grow- 
ing in  moist,  tropical  climates,  in  the  promo- 
tion of  transpiration  at  night. 

The  silvery  areas  not  only  warm  up  slowly 
but  they  also  radiate  heat  less  rapidly  than  a 
typical  leaf,  and  the  higher  temperature  of 
these  areas  after  sunset  promotes  transpira- 

3.  Transverse  section  of  a  velvety  leaf  of  Piper  porphyr- 
acexim.  A  layer  of  aqueous  tissue  lies  next  the  epidermis  of  the 
upper  and  lower  sides.  The  anthocvan  is  in  the  lower  half  of 
the  leaf. 

■!■.  Mottled  leaf  of  Begonia  falcata.  a.  Transverse  seetion 
of  a  brownish  green  velvety  shining  portion  of  lamina.  The 
epidermal  cells  of  the  upper  side  are  furnished  with  papillose 
extensions.  The  epidermal  and  sub-epidermal  layers  are  joined 
without  intercellular  spaces.  The  epidermis  of  the  lower  side 
and  the  spongy  parenchyma  contain  anthocyan.  b.  Trans- 
verse section  through  a  silvery  portion.  The  outer  walls  of 
the  epidermis  are  plane.  Large  air  spaces  are  present  between 
the  epidermis  and  the  cells  containing  chlorophyll. 

^.  Transverse  section  of  a  bright  spot  on  the  leaf  of  Ranun- 
culus ficarioides.  The  sub-epidermal  cells,  a,  contain  a  few 
small  chloroplasts,  and  are  seiDarated  from  the  layer  beneath 
by  large  air-spaces. 

6.  Papillose  epidermal  cells  of  Begonia  imperialis,  var. 
smaragdina,  seen  from  above  by  refracted  light.      After  Stahl. 


Silvery  areas 


LIVING  PLANTS 


tion  at  a  time  when  it  is  at  a  minimum  in  nor- 
mal leaves.  This  is  an  adaptation  of  great 
importance  in  certain  regions  as  is  indicated 
by  the  great  number  of  species  in  which  it  is 
found.  Begonia,  Anthurium,  Dracaena,  Tra- 
descantia,  and  Geranium  offer  examples  of 
this  arrangement. 

The  relation  of  silvery  areas  to  light  may 
be  demonstrated  if  the  lower  side  of  a  mottled 
leaf  of  Begonia  or  Anthurium  is  coated  with 
cocoa  butter  or  lard  and  allowed  to  cool.  If 
the  upper  side  is  exposed  to  sunlight,  the  oily 
substance  will  melt  under  the  green  areas  be- 
fore that  beneath  the  silvery  regions  is  effected. 
If  the  experiment  is  continued  until  all  of  the 
substance  is  melted  and  then  taken  into  a 
shaded  place  to  cool  it  will  be  found  that  the 
butter  opposite  the  silvery  areas  remains 
melted  after  that  on  the  green  portions  has 
solidified.  The  silvery  areas  of  the  leaves 
carry  on  food-formation  less  rapidly  than  the 
green  regions  because  of  the  great  obstruction 
to  penetration  by  liglit. 

Many  leaves  exhibit  a  rich  velvety  surface 
that  is  also  due  to  structural  modifications; 
when  combined  with  underlying  layers  of 
color  as  in  Cissus,  the  effect  is  very  striking. 
The  velvety  appearance  is  due  chiefly  to  the 
papillose  extension  of  the  outer  walls  of  the 
epidermal    cells.     The    conical    and    convex 


outer  walls  act  as  lenses  in  directing  all  rajs 
of  light,  which  strike  the  surface  at  any  angle, 
into  the  interior,  and  in  some  instances  actu- 
ally focusses  them  upon  the  chloroplasts. 
Such  an  arrangement  is  to  be  found  chiefly  in 
plants  native  to  moist  climates,  and  gener- 
ally growing  in  diffuse  light.  Oxalis  aceto- 
sella,  Cissus  discolor,  Fucshia  triphylla,  Mar- 
anta  zevlina,  and  some  begonias  are  exam- 
ples showing  this  adaptation. 

A  plant  or  even  a  single  leaf  may  exhibit 
colors  due  to  several  causes.  Thus  the  leaf 
of  Begonia  falcata  has  silvery  areas  of  the 
usual  structure,  brownish  green  patches  in 
which  the  epidermal  cells  of  the  upper  side  are 
outwardly  convex,  and  those  of  the  lower  side 
contain  anthocyan.  Arrangements  of  this 
character  are  most  frequent  in  the  foliage  of 
tropical  plants.  The  contents  of  the  foregoing 
paper  may  be  briefly  summarized  in  the  fol- 
lowing paragraphs. 

Colors  may  serve  as  an  attractive  or  guid- 
ing device  to  lure  animals  to  flowers  or  away 
from  them.  Physiological  causes  have  played 
the  principal  part  in  the  development  of  pig- 
mented regions,  and  this  development  may 
have  been  modified  by  the  selective  power  of 
animals  to  some  extent.  The  color  sense  is 
lacking  in  some  pollen  carrying  insects,  and 
when  present  has  been  acquired  in  a  compar- 


Conclusions 


LIVING  PLANTS 


ativel^^  recent  period  in  the  history  of  plants. 
Form  and  odor  are  much  more  efficient  agents 
than  color  in  the  attraction  of  animals. 

Chloroph3dl  converts  light  into  energy  by 
the  aid  of  which  the  protoplasm  which  con- 
tains it  is  able  to  bnild  up  complex  foods. 

The  lipochromes  are  found  in  leaves  and 
other  organs,  associated  with  chlorophyll  un- 
der the  name  of  xanthophyll,  in  citrus  fruits, 
in  some  underground  members  and  in  fungi 
and  bacteria.  The  yellow  tints  of  autumn 
leaves  are  due  to  lipochromes.  These  sub- 
stances may  occur  in  solid  crystalloids  in  the 
cell  or  diffused  throughout  the  protoplasm  or 
suspended  in  oily  drops.  The  lipochromes 
probably  serve  as  reserve  substances  in  some 
plants  and  in  others  as  a  screen  against  in- 
tense illumination.  Bacteria  furnished  with 
a  lipochrome  pigment  are  able  tooccludecom- 
paratively  large  quantities  of  oxygen  which 
may  be  given  off  under  partial  pressure.  Cer- 
tain green  and  red  bacteria  are  able  to  carry 
on  food  formation  by  means  of  a  pigment  re- 
sembling chloroph\dl  in  physical  and  chemi- 
cal properties.  A  second  pigment  which  has 
some  of  the  characteristics  of  the  red  color  of 
the  algae  is  also  present  in  these  forms.  The 
pigments  of  the  bacteria  have  been  the  subject 
of  but  little  investigation. 


Anthocyan  is  the  most  widely  distributed 
coloring  substance.  It  occurs  in  solution  in 
cell  sap,  varies  from  red  to  blue  and  violet  and 
may  be  present  in  any  part  of  the  plant.  It 
may  serve  as  a  screen  against  the  disintegrat- 
ing action  of  light  on  chlorophyll  and 
other  nitrogenous  substances.  By  its  heat- 
developing  power  metabolism  and  transpira- 
tion may  be  promoted. 

The  coloring  matter  in  marine  algcC  may 
act  as  a  screen  against  light  and  promote 
metabolism  and  growth  iDy  the  development 
of  heat. 

The  silvery  or  white  appearance  of  organs 
is  due  to  the  loose  arrangement  of  the  cells. 
This  arrangement  serves  as  a  protection 
against  intense  sunhght  and  is  found  in  plants 
growingin  heated  deserts.  The  same  arrange- 
ment may  promote  transpiration  in  plants 
growing  in  moist  shady  situations  with  cool 
nights  or  frequent  rains. 

The  velvety  appearance  of  surfaces  is  due  to 
the  papillose  extensions  of  the  outer  walls  of 
the  epidermis.  The  extended  walls  serve  as 
lenses  to  entrap  sunlight  and  focus  it  upon 
the  chloroplasts.  This  adaptation  is  most 
useful  to  plants  growing  in  diffuse  light. 

Besides  all  of  the  occurrences  of  pigments 
noted  above,  colored  substances  often  are 
found  in  the  walls  of  dead  cells,   as  in  the 


LIVING  PLANTS 


wood  of  Haematoxylon  (logwood)  and 
other  plants,  in  excretions  and  elsewhere  in 
such  manner  as  to  have  no  physiological  sig- 
nificance. The  color  in  such  instances  is  to  be 
regarded  as  a  by-product  in  the  necessary 
chemical  processes  of  the  organism. 


XI. 

THE  RIGHT  TO  LIVE.* 

When  we  come  to  think  of  it,  it  is  strikingly 
patent  that  the  world  was  not  fashioned  to 
especially  promote  the  convenience  and  happi- 
ness of  individuals.  Should  we  assume  such  an 
hypothesis  what  explanation  could  be  offered 
for  the  prevalence  of  parasitism,  by  which  the  of^^nts^ 
individuals  of  one  species  of  animal  or  plant 
live  upon,  and  at  the  expense  of  the  individu- 
als of  another  species,  or  what  could  be  said 
in  extenuation  of  the  carnivorous  habit,  or 
even  of  the  herbivorous  habit  ?  We  find  that 
plants  as  well  as  animals  are  no  respecters  of 
personal  liberty.  The  glittering  tentacles  of 
the  sundews  encompass  the  struggling  fly,  and 
reduce  the  exquisitely  developed  body  to  a 
reeking  paste,  and  bring  to  nought  its  enjoy- 

*Read  before  the  Parlor  Club,  an  organization  devoted  to 
literary  and  scientifie  culture,  Lafayette,  Ind.,  Sept.  17,  1897. 


LIVING  PLANTS 


Likeness  of 
plants  and 
animals 


ment  of  air  and  light  and  fragrance.  And 
there  is  a  travest}^  upon  human  cruelty  enact- 
ed by  those  curious  swamp  plants  of  North 
Carolina,when  they  clasp  their  bristling  leaves 
together  over  the  incautious  insect  with  the 
same  blasting  results  to  the  mortal  life  of  the 
prisoner  as  befell  the  unfortunate  victims  of 
inquisitorial  times  who  succumbed  to  the 
deadly  embrace  of  the  eiserne  Jungfrau.  When 
standing  in  the  castle  tower  at  Nuremberg, 
viewing  this  torture  weapon  of  mediaeval  in- 
genuit^^  onecannot  but  feel  that  here  the  God- 
like powers  of  man  dropped  perilously  near 
the  blind  forces  of  lower  nature. 

In  all  tlie  essentials  that  go  to  constitute  a 
living  organism  of  whatever  degree  of  com- 
plexity, that  is,  the  ability  to  take  food,  to 
grow,  to  respond  to  stimulation  and  to  ex- 
hibit spontaneous  and  directive  energies,  the 
plant  is  the  Ishmaelitic  branch  of  the  same 
great  world's  family  in  which  the  animal  has 
acquired  a  higher  standing  by  superior  aware- 
ness. In  other  words,  the  plant  and  the  ani- 
mal, in  ultimate  essentials  are  of  like  consti- 
tution. It  is  evident,  therefore,  that  the  argu- 
ment for  natural  rights  may  be  supported 
from  either  branch  of  the  organic  phylon ; 
bearing  in  mind,  however,  that  in  shifting 
Irom   the  animal   to  the  plant,  or  from  the 


THE  RIGHT  TO   LIVE 


plant  to  the  animal,  the  alluring  quicksands 
of  bare  analogy  must  be  sedulously  avoided. 
Turning  from  the  dramatically  tragic  phases 
of  plant  life,  let  us  look  at  the  everyday  condi- 
tions of  existence.  Two  prominent  factors  in 
plant  as  well  as  in  animal  life,  are  the  rate  of 
increase  and  the  supply  of  food.  In  regard  to 
these  some  simple  calculations  will  be  helpful, 
although  they  may  prove  a  cabala  that  will 
disenchant  and  spread  before  us  a  different 
panorama  from  the  quiet,  pastoral  repose, 
which  we  confidently  anticipate  when  we 

"  Go  forth  under  the  open  sky,  and  list 
To  Nature's  teachings." 

Linnaeus  computed   the  progeny  of  an  an- 
nual plant,  from  which  only  two  seeds  grew 

into  plants  the  second  year,  and  from  each  of    t>     -t-t 

^  -^         '  Possible  rate 

these  two  plants  two  others  sprung  up  the  of  increase 
third  year,  and  so  on  for  twenty  years.  This 
is  a  very  low  rate  of  increase,  yet  at  the  end 
of  the  second  decade  the  one  original  plant 
would  be  represented  by  a  million  offspring. 
A  computation  made  by  Huxley  gives  a  some- 
what clearer  illustration  of  the  real  tendency 
of  plant  life.  By  the  terms  of  his  supposition 
fifty  seeds  are  able  to  make  a  successful 
growth  from  each  plant  of  the  preceding  year, 
and  a  plant  for  full  development  is  permitted 
to  have  one  square  foot  of  ground.  Now  es- 
timating that  the  whole  land   area  of  the 


LIVING  PLANTS 


world  in  round  numbers  is  fift\^-one  million 
square  miles,  and  supposing  for  the  sake  of 
the  illustration,  that  every  foot  of  this  ground 
is  free  from  all  encumbrance  and  equally 
capable  of  supporting  plant  life,  we  shall 
arrive  at  the  astounding  result  that  a  single 
parent  plant  b^^  the  tenth  year  will  have 
given  rise  to  enough  plants  to  occupy  every 
foot  of  this  great  area,  and  over  five  hundred 
thousand  billions  besides.  This  means  that 
an  annual  plant,  increasing  at  a  fifty-fold  rate, 
has  the  capacity  to  supply  a  plant  for  every 
eight  square  inches  of  land  surface  of  the 
whole  globe  within  one  decade. 

Such  marvelous  results  of  fecundity  are  al- 
most past  belief,  and  it  is  worth  while  to 
inquire  if  any  facts  exist  that  give  counten- 
ance to  such  deductions.  The  ubiquity  and 
prolificacy  of  weeds  are  proverbial,  but  upon 
closer  acquaintance  even  the  popular  fancy 
seems  scarcely  to  reach  the  realitj^,  to  judge 
from  the  records.  Sturtevant  found  that  a 
plant  of  shepherd's  purse,  one  of  the  most 
common  and  most  insignificant  of  weeds,  bore 
fully  12,000  seeds,  that  a  plant  of  burdock 
had  40,000  seeds,  and  that  a  number  of  other 
common  weeds  were  equally  fertile.  But  the 
list  that  he  examined  reached  its  climax  in 
the  purslane,  a  plant  which  by  its  obtrusive- 
ness  and  pertinacity  has  become  the  symbol 


THE  RIGHT  TO  I.IVE 


of  offensiveness— "  as  mean  as  pusley,"  the 
saying  goes.  A  single  plant  of  this  species 
bore  over  two  million  seeds,  surely  a  marvel- 
ous prodigality.  And  yet  even  these  great 
numbers  are  certainly  not  the  full  measure  of 
the  plant's  capacity,  for  some  seeds  may  have 
dropped  off  before  the  time  of  counting,  and 
many  more  might  still  have  ripened  if  the  in- 
terests of  science,  or  other  untoward  circum- 
stances, had  not  cut  sliort  a  flourishing  career. 
But  weeds  are  not  the  only  ijlants  to  show 
a  superfluity  of  seeds.  How  many  seeds  do  Prolificacy  of 
you  think,  are  borne  on  a  single  beech  tree,  other  plants 
or  even  an  oak?  Certainly  many  hundreds 
more  than  ever  grow  into  trees.  And  the 
grasses,  and  climbers,  and  shrubs,  and  the 
numerous  wayside  plants  that  individually 
affect  our  lives  so  little  that  we  do  not  know 
them  by  name,  does  it  not  seem  safe  to 
assume  that  they  are  potentially  capable,  to 
be  conservative,  of  a  fifty-fold  annual  increase, 
rising  in  not  a  few  instances  to  many  thous- 
and-fold, and  sometimes  to  a  million-fold? 
But  the  productive  spots  are  already  occu- 
pied, and  outside  of  cultivated  lands  largely 
with  perennial  plants,  so  that  there  is  little 
chance  of  even  one  out  of  the  large  number  of 
offspring  finding  conditions  for  average  devel- 
opment. What  becomes  of  the  other  49,  or 
999,  or  999,999  ?      Many  never  find  the  op- 


LIVING  PLANTS 


portunity  for  germination  and  perish  without 
feeling  conscious  hfe;  but  many  others  do 
start  and  attain  some  size  only  to  be  starved 
and  smothered  out  of  existence. 

The  condition  of  the  plant  world  may  be 
likened  to  the  American  struggle  for  riches; 
a  very  few  become  millionaires,  a  small  mi- 
nority attain  financial  independence,  but  the 
great  majority  die  without  knowing  the  com- 
forting security  of  a  competence.  It  has 
become  customary  to  speak  of  this  over- 
whelming failure  to  attain  a  favorable  posi- 
tion in  the  world  as  a  warfare,  and  to  some 
extent  the  term  is  applicable;  it  is  an  un- 
organized warfare,  the  fighting  of  a  mob 
where  there  is  no  leadership,  or  to  select  a  yet 
better  simile,  the  frantic  efforts  of  individuals 
under  the  excitement  of  a  panic  where  action 
is  controlled  by  the  single  desire  to  find  per- 
sonal safety.  Darwin's  striking  phrase,  "  the 
struggle  for  existence,"  which  has  been  so 
much  used,  and  also  greatly  abused,  seems 
applicable  enough  when  we  think  that  for 
each  plant  that  attains  normal  development 
thousands  perish.  As  in  the  panic,  it  is  the 
strongest  ones,  or  those  having  most  advant- 
ageous positions,  or  who  are  most  apt  in 
adapting  themselves  to  passing  conditions, 
that  survive ;  and  in  this  sense  Herbert  Spen- 
cer's twin  phrase,  the  "survival  of  the  fittest" 


THE  RIGHT  TO  LIVE 


finds  its  application.  It  is  the  same  in  all 
essential  particulars  with  animals  as  with 
plants,  there  is  a  constant  struggle  for  a 
suitable  portion  of  food  and  a  comfortable 
amount  of  space,  the  fortunate  few  succeed- 
ing, while  multitudes  perish.  To  this  general, 
coercive  law  of  the  organic  world  man  finds 
in  himself  no  exemption,  except  in  so  far  as 
the  humanizing  principle  of  altruism  has 
eifect.  Thus  throughout  the  world  the  truth 
in  the  refrain  of  Grant  Allen's  "Ballade  of 
Evolution  "  finds  confirmation  : 

"  For  the  fittest  will  always  survive, 
While  the  weakliest  go  to  the  wall." 

All  are  aware  of  the  substantial  use  Darwin 
made  of  facts  regarding  nature's  prodigality 
in  animate  forms,  and  the  resulting  competi- 
tion between  them,  in  establishing  his  theory 
of  the  origin  of  species.  The  logical  result  of 
the  theory  requires  the  subordination  of  the 
individual  to  the  good  of  the  race.  As  of  all 
the  myriad  individuals  only  the  fittest  survive, 
the  race  is  in  consequence  gradually  improved. 
The  battle  is  to  the  strong,  and  the  weak  are 
mercilessly  shoved  aside,  oppressed,  and  an- 
nihilated. There  seems  no  escape  from  the 
conclusion  that  the  ethics  of  nature  make 
right  and  might  synonymous  terms.  Individ- 
uals not  onh'  crowd  and  overpower  individ- 
uals of  the  same  species,  but  they  pre3^  upon 


LIVING  PLANTS 


those  of  other  species  to  an  extent  scarcely 
conceivable.       All    the      tribes    of    parasitic 
A  world  fungi   draw   their  sustenance   from    the    liv- 

of  strife  "ig  host,   and  give  rise  to  the  long  category 

of  plant  ills  known  as  rusts,  smuts,  mildews, 
rots,  molds  and  blights.  The  minutest  veg- 
etable parasites,  the  bacteria,  attack  and 
bring  low  the  largest  and  most  noble  forms 
of  both  kingdoms,  especially  being  man's 
most  insidious  and  deadly  enemies.  With 
comparatively  few  exceptions  animals  of 
high  and  low  degree,  of  all  sizes,  forms  and 
habits,  whether  inhabiting  water,  earthor  air, 
from  the  microscopic  amoeba  to  the  bear  and 
the  elephant,  seize  upon  and  devour  in  part  or 
in  whole  other  living  beings,  in  order  to  main- 
tain their  own  existence.  Not  only  does  the 
lion  kill  other  beasts  of  the  jungle,  the  wolf 
seize  the  lamb,  the  owl  eat  the  mouse,  and  the 
robin  the  earthworm,  but  the  ox  feeds  upon 
the  living  grass,  the  sparrow  gourmandizes 
upon  myriads  of  young  plants  in  the  seed 
stage,  and  the  caterpillar  defoliates  trees. 
With  the  exception  of  the  carrion  beetle,  the 
house  fly,  the  nectar- feeding  humming  bird, 
and  some  others,  the  animal  world  finds  its 
daily  food  by  destroying  the  life  of  other 
weaker  beings,  sometimes  animal,  sometimes 
plant  life  being  preferred.  In  this  wholesale 
destruction   of  life  man  lends  a  ready  hand. 


THE  RIGHT  TO  I.IVE 


life  for  a  dinner 


He  has  introduced  the  refinement  of  refrain- 
ing from  eating  his  fellow  man,  ])ut  he  usually 
does  not  scruple  to  partake  of  any  other 
kind  of  flesh  that  suits  his  palate,  and  never 
thinks  of  hesitating  when  plant  life  is  in  ques- 
tion. He  has  advanced  so  far  as  to  cook 
much  of  his  food,  but  he  still  enjoys  a  live 
oyster,  and  munches  live  celery,  radishes  and 
lettuce  with  a  satisfaction  that  denotes  utter 
absence  of  sensitiveness  regard  hig  the  exercise 
of  his  rights.  It  occurred  to  me  to  notice 
how  many  individual  lives  were  destroyed 
to  furnish  me  a  dinner  to-day.  The  beef  Destruction  of 
and  the  fowl  required  two  animal  liveK. 
There  were  over  a  hundred  lima  beans,  some 
six  or  seven  hundred  kernels  of  green  corn, 
part  of  two  or  three  Irish  and  sweet  potatoes, 
many  hundred  grains  of  wheat  for  the  bread, 
and  still  greater  numbers  of  yeast  cells  to 
lighten  it.  I  did  not  count  the  number  of 
seeds  in  the  sliced  tomato,  and  do  not  know 
how  many  grains  were  required  for  the  cup 
of  coffee,  neither  can  I  well  estimate  the  num- 
ber of  bacteria  that  took  part  in  flavoring 
my  piece  of  cheese,  and  which  were  smother- 
ed in  the  curing  process.  It  was  a  simple  re- 
past, and  yet  to  supply  it  required  the  sacri- 
fice of  a  thousand  or  more  individual  lives, 
exclusive  of  the  yeast  and  bacteria. 

Was  there  anything  wrong  in  this  destruc- 


202  LIVING   PLANTS 

Natural  ri  ht       ^^^"  °^  ^^^^  ^^  furnish  a  meal  for  one  individu- 
to  food  'il  ?     Would  it  have  been  anymore  or  any  less 

wrong  to  have  eaten  onl^^  animal  food,  or 
only  vegetable  food  ?  Is  there  anything 
wrong  in  the  owl  eating  a  mouse  or  in  the 
rabbit  eating  herbage?  Evidently  the  an- 
swer is  clear  and  direct.  Every  being  is  enti- 
tled by  the  very  law  of  its  nature,  and  by  the 
constitution  of  the  organic  world,  to  the  food 
needed  for  its  sustenance,  and  animal  life  per 
se  is  no  more  sacred  than  vegetable  life.  This 
destruction  of  one  being  by  another  is  in  fact 
the  only  method  by  which  the  balance  of  life 
on  the  earth  can  be  maintained;  indeed,  all 
existence  is  vicarious,  many  lives  are  sacrificed 
to  maintain  the  few. 

The  evolutionary  argument,  which  has  now 
been  illustrated,  runs  along  two  lines  pointed 
out  by  Malthus  nearly  a  century  ago,  neither 
favoring  the  individual.  On  the  one  hand  ex- 
cessive increase,  and  on  the  other,  necessity  for 
food,  cause  a  dire  struggle  for  existence,  in 
which  the  race  is  benefited,  but  the  individual 
is  generalh'  worsted .  From  this  point  of  view 
Logic  of  the  only  right  to  live  that  an  individual  being 

goo  orune  can  claim  is  vested  in  its  chance  possession  of 
strength  and  opportunity ;  it  lives  merely 
through  good  fortune. 

If  we  inquire  into   the  object  of  living,  we 
shall  find  that  the  evolutionists,  the  pre-evo- 


THE  RIGHT   TO  LIVE 


lutionists  and  the  creationists  are  essentially 
united  in  opinion.  The  chief  end  of  existence  Object 
is  to  bear  offspring  that  the  race  may  be  per-  of  living 
petuated,  they  all  say  directly  or  indirectly. 
From  the  highest  forms  to  the  lowest,  through 
both  the  plant  and  animal  series,  this  is  held 
to  be  sufficiently  patent.  Again  the  individual 
is  sacrificed  to  the  good  of  the  race.  In  regard 
to  plants  this  seems  to  have  alwa3^s  been 
accepted  as  a  matter  of  course.  I  might 
quote  confirmatory  statements  without  end, 
but  will  only  give  two.  Cesalpino,  one  of  the 
wisest  of  early  botanists,  said  that  "the 
final  purpose  of  plants  consists  in  that  pro- 
pagation which  is  effected  by  the  seed,"  and 
it  would  be  difficult  to  find  any  author  who 
disagreed  with  him  from  that  time  to  the 
present.  It  is  so  generally  accepted  that  one 
should  not  be  surprised  that  it  is  taught  to 
children  as  an  unquestioned  fact.  In  one  of 
Mrs.  William  Starr  Dana's  recent  nature 
books  for  young  readers,  a  whole  chapter  is 
devoted  to  the  topic,  "  What  a  plant  lives  for," 
with  the  terse  conclusion  that  "a  plant  lives 
to  bear  seed." 

Here  is  the  philosophy  of  the  ages  regarding 
earthly  existence  in  a  nutshell ;  but  to  me  it  is 
a  very  unsatisfactory  philosophy.  I  do  not 
see  why  one  may  not  argue  that  it  is  founded 
upon  an  absurdity,  for  it  is  equivalent  to  say- 


LIVING  PLANTt 


ing  that  the  chief  reason  for  living  is  to  die 
that  another  may  live,  and  that  other  must 
in  turn  do  the  same;  thus  true  fruition,  com- 
plete realization,  is  never  attained,  but  is 
always  in  the  unreachable  future. 

A  misconception  prevails,  it  appears  to  me, 
in  regard  to  the  place  that  death  and  repro- 
duction hold  in  the  economy  of  the  world, 
which  has  thrown  us  upon  a  wrong  track. 
We  may  safely  assume  that  much  of  the  di- 
versity in  the  mode  and  form  in  which  life  is 
presented  to  us  has  resulted  from  the  changea- 
bleness  and  uncertainty  of  external  conditions. 
If  moisture,  warmth  and  food  could  be,  and 
especially  if  they  had  always  been,  supplied 
to  every  organism  in  uniform  and  ample 
amount,  the  struggle  for  existence  would  pre- 
sent altogether  another  phase  from  its  present 
day  aspect. 

If  the  moisture  of  air  and  soil  were  of  ap- 
proximately unvarying  percentage  from  day 
to  day,  and  year  to  year,  and  if  warmth  were 
maintained  at  the  genial  glow  of  a  summer 
day  without  interruption,  the  provisions 
against  drouth  and  cold,  shown  in  seeds, 
tubers,  bulbs,  resting  spores,  sclerotia  and 
similar  protective  devices,  would  be  largely 
purposeless,  and  could  not  long  persist,  in 
fact  might  never  have  developed.  Under  such 
favorable  conditions  for  continuous  growth, 


THE  RIGHT  TO  LIVE 


without  the  necessity  of  providing  for  the  in- 
terpolation of  inhibiting  periods  of  vi'inter 
cold  or  summer  dryness,  the  larger  part  of 
productive  activity  would  doubtless  disap- 
pear, and  with  it  much  of  the  fierce  strife  for 
place. 

If  added  to  other  favorable  conditions  for 
existence  an  adequate  supply  of  food  were 
available,  we  can  well  believe  that  organisms 
might  become  potentially  immortal,  that  is, 
they  might  live  indefinitely  unless  killed  by 
pure  accident.  Such  a  happy  environment 
would  be  a  true  vale  of  Avalon: 

"Where  falls  not  hail,  orraiii,  or  auy  snow, 
Nor  ever  wind  blows  loudly;  butit  lies 
Deep-meadow'd,  happy,  fair  with  orchard  lawns 
And  bowery  hollows  crown'd  with  summer  sea." 

It  would,  however,  be  a  land  of  continuous 
youth,  a  Ponce  de  Leon  realization,  rather 
than  a  haven  for  effete  King  Arthurs. 

Weismann  finds  an  argument  leading  to  the 
like  conclusion  in  the  fission  reproduction  of 
many  unicellular  animals,  by  which  no  part  of 
the  organism  dies  during  the  process  of  mul- 
tiplication, but  each  part  expands  into  the 
perfection  of  an  individual.  A  not  materially 
dissimilar  process  among  higher  members  in 
the  vegetable  kingdom  is  the  ready  propaga- 
tion by  successive  branching  of  such  rhizo- 
matous  plants  as  certain  ferns,  iris  and 
grasses.   As  the  burrowing  plant  body  pushes 


206  LIVING  PLANTvS 

forward  in  its  growth  the  living  contents 
of  the  rear  cells  are  gradually  withdrawn, 
and  the  effete  skeleton  of  cell-walls  disinte- 
grates ;  and  in  a  similar  way  the  appendages 
of  leaf  and  root  serve  their  purpose  and  are 
discarded,  as  a  stag  sheds  his  antlers.  Al- 
though leaf  and  root  and  posterior  part  of 
stem  repeatedly  disappear  the  plant  retains 
its  identity  as  an  individual.  When  the  drop- 
ping away  of  the  end  of  the  rhizome  has 
involved  a  branch,  the  two  advancing  ends 
become  entirely  separate  individuals,  a  method 
of  increase  that  some  species  find  so  efficient 
that  they  rarely  or  never  produce  seeds  or 
even  flowers.  It  is  no  fiction  to  say  that  such 
a  plant  never  dies.  It  is  compelled  to  drop  its 
appendages  and  hibernate  during  the  incle- 
ment season,  but  its  ph^'siognomy  remains 
the  same  whatever  age  it  may  attain. 

It  has  been  shown  in  a  previous  essay  (page 
101),  that  increasing  the  food  supply,  or  of 
other  external  factors  favorable  to  growth, 
tends  to  prolong  the  life  of  the  individual 
and  to  decrease  the  amount  of  reproduction. 
This  is  evidently  moving,  although  but  a  step, 
in  the  direction  of  ideal  conditions  for  the 
even  display  of  vital  energy. 

These  and  other  reasons  which  can  not  find 
place  here  lead  us  to  think  that  both  seniHty 
and  excessive  increase  are  not  inherent  char- 


THE  RIGHT  TO  LIVE 


acteristics  of  life,  but  have  arisen  to  meet  the 
demands  of  existence  in  a  too  changeable 
world,  and  that  even  death  is  a  "concession 
to  the  outer  conditions  of  life."  Natural 
death  may  be  regarded  as  a  phylogenic  inci- 
dent, and  accidental  death  as  an  ontogenic 
incident. 

The  argument  here  outlined,  but  which  can 
not  be  adequately  developed,  is  intended  to 
show  that  reproduction  is  partly,  and  death 
wholly  an  adaptation,  and  that  these  can  no 
more  be  said  to  be  the  purposes  of  living 
than  can  other  adaptations,  such  as  the  an- 
nual production  of  winter  buds  on  trees,  and 
on  such  herbaceous  plants  as  the  tiger  lily. 
Furthermore,  the  logic  of  excessive  increase 
and  consequent  inadequacy  of  food  does  not 
warrant  us  in  assuming  that  present  forms 
of  existence  do  not  possess  a  natural  right  to 
the  greatest  longevity  and  fullest  develop- 
ment which  their  individual  opportunities 
permit  them  to  secure.  The  individual  is  lim- 
ited in  the  duration  of  its  active  period  and  in 
the  expenditure  of  its  energies  by  the  inherited 
adaptations  imposed  by  the  conditions  under 
which  its  ancestry  has  lived,  and  these  limita- 
tions are  necessarily  passed  on  to  its  off- 
spring, but  its  right  to  the  full  measure  of  its 
opportunities  for  self-development  can  not 
therefore  be  withheld.      It  must  be  true  that 


Plants  are 
born  to  live 


LIVING  PLANTS 


being,  everyday  existence,  is  an  end  in  itself. 
"Plants  are  born  to  live,  not  to  die,"  says  L. 
H.  Bailey  in  his  work  on  the  survival  of  the 
unlike,  and  the  same  is  undoubtedly  true  of 
animals  and  of  man. 

If  I  have  made  good  my  argument,  the  in- 
dividual has  a  right  to  its  life,  it  has  a  right 
to  live,  although  under  the  present  conditions 
Right  to  life        it  must  maintain  its  position   and  its  life  by 
should  be  force.    And  if  the  individual  has  a  right  to  its 

respected  \\{q^  and  if  the  purpose  of  that  life  is  primarily 

to  give  enjoyment  to  the  possessor,  there  is 
after  all  a  sacredness  about  life  that  makes  it 
wrong  to  destroy  it  needlessly.  Not  only  the 
animal,  but  also  the  plant  is  entitled  to  con- 
sideration. 

"Life  is  not  to  be  bought  with  heaps  of  gold. 
Not  all  Apollo's  Pythian  treasures  hold, 
Or  Troy  once  held,  in  peace  and  pride  of  sway, 
Can  l)ril)e  the  poor  possession  of  a  day." 


XII. 

THE  DISTINCTION  BETWEEN  ANIMALS  AND  PLANTS.* 

No  classes  of  natural  objects  seem  to  the 
general  apprehension  more  distinct  and  im- 
miscible than  animals  and  plants.  The  free 
moving  intelligent  animal  appears  immeas- 
urably removed  from  the  fixed  insentient 
plant. 

Yet,  underlying  this  seeming  distinctness, 
there  usually  lurks  some  vague  feeling  of 
analogy  between  the  hidden  springs  of  life  in 
the  two  classes  of  beings.  Strange  flights  of 
the  imagination  have  imposed  themselves 
upon  belief  in  all  ages,  that  are  hard  to  ac- 
count for  unless  we  take  this  general  feeling 
of  a  unity,  or  possibility  of  transference  be- 

*A  paper  read  before  the  joint  session  of  the  sections  of 
botany  and  zoology  of  the  American  Association  for  the  Ad- 
vancement of  Science,  at  the  Springfield  meeting,  September  2, 
1895,  and  printed  inthe  AiHer/caa  ATatHra/ist,  November,  1895; 
somewhat  revised  and  extended. 


LIVING  PI-ANTS 


Learned 
vagaries 


tween  the  essential  natures  of  the  two  classes 
of  objects,  to  be  deep-seated  and  almost  uni- 
versal. Only  two  or  three  centuries  ago  there 
were  even  learned  men  who  believed  in  the 
Scythian  lamb,   that  grew   on   the  top  of  a 


Fig.  21. — The  Scythian  lamb,  that  vegetated  like  a  tree, 
but  ate  herbage.  It  was  reputed  to  flourish  on  the  salt  plains 
west  of  the  Volga.  Cut  reproduced  from  Claude  Buret's  "His- 
toric des  Plantes,"  1605. 

small  tree-trunk  in  place  of  foliage,  and  in  the 
wonderful  tree  of  the  British  Isles,  whose  fruit 
turned  to  birds  when  it  fell  upon  the  ground, 
and  f.o  fishes  when  it  fell  into  water.  In  still 
earlier  times,  even  more  astonishing  vagaries 
were  accepted  as  common  knowledge,  es- 
pecially when  vouched  for  by  travelers. 
But  naturalists  and  others,  who  withheld 


PLANTS  AND  ANIMAL.S 


Fig.  22. — The  treeof  the  British  Isles,  prodiicingboth  fishes 
and  birds.  Gerarde  and  other  eminent  natiiralists  describe 
it  with  confidence.  Cut  reproduced  from  Buret's  "Historic 
des  Plantes,"  1605. 


212  LIVING  PLANTS 

belief  in  the  fabulous  tales  about  strange  be- 
ings in  far  off  lands,  such  as  Pliny  describes 
in  his  Natural  History,  and  were  able  to  keep 
their  love  of  the  marvelous  within  bounds, 
Ancient  and  to  found  their  conceptions  so  far  as  pos- 

opinions  sible  upon  verifiable  observations,  held  more 

rational  and  clearer  views  of  the  two  king- 
doms. As  a  consequence  of  direct,  although 
not  extended,  observation  the  separation  of 
the  higher  animals  and  plants  appeared  to 
most  persons  of  bygone  times,  as  well  as  of 
today,  simple  enough.  The  free,  independent 
movements  of  animals,  well  directed  toward 
evident  ends,  and  plainW  originating  from  in- 
ternal impulses,  have  from  such  a  standpoint 
fully  entitled  them  to  be  called  animate  ob- 
jects ;  while  plants,  deprived  of  the  power  of 
moving  about,  seemingly  without  feeling,  and 
to  all  appearance  incapable  of  conscious  re- 
action, could  only  be  described  as  living,  as 
animate,  only  by  an  extension  of  terms,  and 
certainly  not  as  sentient. 

It  does  not  take  a  very  wide  acquaintance 
with  living  nature,  however,  to  become  aware 
that  freedom  of  movement  and  fixit\'  of  posi- 
tion are  not  distinctive  characters  of  animals 
and  plants  respectively,  and  that  even  the 
possession  of  feeling  does  not  wholly  separate 
them.     Many  centuries  ago,  as  we  learn  from 


PLANTS  AND  ANIMALS 


Aristotle  and  other  ancient  writers,  it  had 
been  observed  that  sponges  grow  attached 
firinl}'  to  rocks  by  root-Hke  extensions,  yet 
possess  some  feehng.  that  sea-cucumbers 
{Holotburin)  and  sea-slugs  (Ctenopbora), 
although  having 
freedom  of  move- 
ment, seem  to  lack 
feeling,  and  in  this 
respect  behave 
like  plants,  that 
sea-anemones  are 
fixed  objects,  yet 
are  sensitive  like 
animals,  and  that 
many  other  living 
things  have  char- 
acteristics that 
make  them  in  like 
manner  uncertain 
of  classification. 
Aristotle's  conclu- 
sion from  these 
facts,  that  "na- 
ture passes  grad- 
ually from  the  insentient  over  to  the  sentient 
through  forms  that  truly  live  but  are  not 
animals,  "  only  ne°ds  the  substitution  of 
Mycetozoa   and   some  Flagellata  for  the  Po- 


FiG.  23 — A  sea  cticnnibcr  with 
extended  branched  ten  t acles. 
(After  Glaus.) 


LIVING  PLANTS 


rifera  and  Coelenterates  as  its  foundation  to 
make  it  acceptable  to  some  students  of  the 
present  day. 

The  citation  of  a  few  opinions  held  bj^ 
modern  savants  regarding  the  ultimate  dis- 
tinction between  animals  and  plants,  although 
necessarily  brief  and  without  the  setting  which 
the  authors  considered  the  justification  for 
their  conclusions, 

will  indicate  how  ^.^        ,  "^ 

numerous    and  "^        '*^ 

vain  have  been  the 
attempts  to  find 
some  character  of 
universal  diag- 
nostic value.  To  Wv  >{; 
some    minds     the  ^^   ^ 

,        y  C  1  Fig-   2+. — A    niycetozoan    {Arcyria 

task   ot    pi'operiy  ^j„^^^j^)  j,j  ^jjg  j.gg,.j,,g  j^t^^g  .attached 

placing     the       ani-  to    bark.      Part  of  the  spore  masses 

,  ,..  ■,  ,       removed,    leaving   their    bases.       lin- 

mal-llke      plants  j^rged  three  diameters.   (After  Engler 

and  plant-like  an-  and  Pranti.) 
imals    has    been 

well  enough  disposed  of  by  creating  an 
intermediate  kingdom.  This  was  first  done 
by  the  Englishman  Wotton  at  the  beginning 
of  the  active  period  that  followed  the  intel- 
lectual stupor  of  the  middle  ages.  In  his 
work  on  the  distinguishing  characters  of 
animals,   "  De  differentiis   animalium,"    pub- 


PLANTS  AND  ANIMALS 


lished  in  1552,  he  established  the  group  of 
plant-animals  or  zoophytes.  These  organisms 
were  subsequently  shown  to  possess  but  a 
superficial  analogy  to  plants,  being  thor- 
oughly animal  in  all  important  respects. 
Most  zoologists  and  botanists  since  the  time 
of  Wotton  have  been  content  to  share  the 
problematical  forms,  either  in  common  or  bj^ 
sufference,  permitting  them  to  be  carried  into 
one  camp  or  the  other  at  the  convenience  or 
pleasure  of  the  student.  A  few  years  ago, 
however,  Hasckel  advocated  an  arrangement 
that  met  with  some  favor.  He  proposed  to 
place  the  simple  intermediate  forms  together 
under  the  heading  Protista,  a  plan  that  time 
shows  has  added  nothing  to  clearness  of  con- 
ception or  convenience  of  study. 

Many  writers  believe  that  no  characters 
can  be  found  that  are  universally  diagnostic. 
Dr.  Asa  Gray  once  said  (1860)  in  connection 
with  an  argument  in  justification  of  Dar- 
winian evolution,  that  in  regard  to  the  two 
classes  of  organisms,  "no  absolute  distinc- 
tion whatever  is  now  known  between  them,    oi    j.       t^u 

.  .  -Ill  rSlenoing  oi  the 

it  is  quite  possible  that  the  same  organism    two  kingdoms 
may  be  both  vegetable  and  animal,  or  may 
be  first  the  one  and  then  the  other."     The 
learned  Dr.  Claus,in  his  prorectoral  address 
before  the  University  of  Marburg  in  1863  on 


LIVING  PLANTS 


the  limits  of  animal  and  plant  life,  after  care- 
fully reviewing  the  whole  subject,  sa3^s  in  his 
concluding  sentence  that  "a  fast  and  abso- 
lute boundary'  between  animals  and  plants 
does  not  exist."  The  last  sentence  of  Profes- 
sor Huxley's  lecture,  delivered  in  London  in 
1876  upon  the  border  territory  between  the 
animal  and  the  vegetable  kingdoms,  breathes 
the  same  sentiment.  It  was  his  opinion  that 
"the  difference  between  animal  and  plant  is 
one  of  degree  rather  than  of  kind,  and  that 
the  problem  whether,  in  a  given  case,  an 
organism  is  an  animal  or  a  plant,  may  be 
cssentialh'  insoluble." 

The  positive  statements  of  such  leaders  of 

thought  require  no  additional  evidence    to 

show  that    finding    crucial    tests  to    apply 

under  all  circumstances  is  well  nigh  hopeless. 

And  yet  the  writer  believes  that  the  last  word 

is  not  said,  and  that  a  clue  will  j'et  be  found 

leading  to  a  reasonably  clear  solution  of  the 

problem. 

Characters  It  has  long  been  recognized  that  characters 

from  structure      drawn  from  structure  are  far  more  reliable  in 

and  function        determining    relationship     than     characters 

drawn  from  function.      The  latter    respond 

more  readily  to  changes  in  the  environment, 

and  therefore  forms  having  little  affinity  mav 

possess  the  same  physiological  adaptations. 


PLANTS  AND  ANIMALvS 


Profound  changes  in  the  environment  event- 
ually bring  about  changes  in  structure ;  but 
they  follow  so  slowly  that  rudimentary  or- 
gans and  various  vestigial  structures  reveal 
the  true  affinities  where  all  other  characters 
fail. 

In  all  serious  attempts  to  fully  distinguish 
the  two  kingdoms,  so  far  as  they  have  come 
to  my  notice,  the  characters  selected  have 
been  essentially  physiological,  and  not  struc- 
tural. Some  of  the  most  noted  of  these  may 
be  brieflj^  mentioned.  Linnaeus  leads  with  his 
classical  aphorism  :  ''Lapides  crescunt,  veget- 
ahilia  crescunt  et  vivunt,  animalia  crescunt, 
vivunt  et  sentient,'^  with  which  he  opened  his 
work  on  philosophical  botany  in  1751. 
Cuvier,  in  the  second  edition  of  his  "Regne 
animal,"  issued  in  1828,  elaborated  four 
reasons  for  the  "division  of  organized  beings 
into  animals  and  vegetables:"  viz.,  the  pos- 
session by  animals  of  (1)  organs  foringestion 
of  food,  (2)  circulatory  system,  (3)  nitrog- 
enous structure  and  (4)  true  respiration,  of 
which  the  first  seemed  to  him  most  important, 
and  did,  indeed,  survive  the  longest.  The 
distinction  advocated  by  Dangeard  (1887), 
Minot  (1895),  and  others,  that  only  animals 
are  capable  of  receiving  solid  food  into  the 
body,  may  be  considered  the  latest  phase  of 


LIVING  PLANTS 


Various 

physiological 

distinctions 


Cuvier's  first  proposition.  Sedgwick  and 
Wilson  in  their  "Biology"  (1886),  find  the 
sole  characteristic  of  animals  to  be  depend- 
ence upon  proteid  food.  Von  Siebold  in  a 
dissertation  upon  this  subject  published  in 
1844,  believed  he  had  found  a  criterion  in  the 
contractility  of  tissues.  Some  have  brought 
forward  the  chlorophyll  function,  or  the  pro- 
duction of  starch,  cellulose,  etc.  The  latest 
suggestion  is  probably  that  of  Conway  Mac- 
Millan  (1895),  who  sees  a  fundamental  dif- 
ference between  animals  and  plants  in  the 
dynamic,  energy -liberating  nature  of  the  for- 
mer, expressed  morphologically  in  cephaliza- 
tion,  and  in  the  static,  energy-fixing  nature 
of  the  latter,  expressed  morphologically  in 
sporophy  tization . 

Whatever  the  characters  that  are  selected 
for  our  crucial  test,  it  is  evident  that  they 
must  apply  equally  to  the  highest  and  most 
complex  forms,  to  the  simplest  unicellular 
forms,  and  to  all  intermediate  grades.  What 
structure  or  structures  are  there  so  universal, 
so  indispensable  to  the  simplest  and  to  the 
most  complex,  to  animal  and  plant  alike,  from 
which  characters  can  be  drawn  of  universal 
application  ?  The  least  complex  organisms 
are  likely  to  furnish  most  readily  the  clue  to 
the  answer.     Setting  aside  physiological  con- 


PLANTS  AND  ANIMALS 


The  most  uni- 


siderations,  and  having  in  mind  the  simplest 
organism,  it  is  evident  as  soon  as  mentioned, 
that  the  first  structure  Hkely  to  be  present, 
aside  from  the  indispensable  cytoplasm  and 
nucleus,  would  be  a  cell  wall.  The  cell  wall  is  versa!  Structure 
the  shield,  the  armor,  the  enveloping  cloak, 
that  the  organism  throws  about  itself  to  pro- 
tect the  living,  delicate  protoplasm  from  the 
rough  contact  and  harmful  influence  of  the 
outer  world.  Some  protection  is  well  nigh 
indispensable  upon  the  free  surfaces.  For  the 
unicellular  organisms  it  is  a  cell  wall;  for  the 
multicellular  organisms  the  walls  about  the 
cells  of  part  or  all  of  the  tissues  persist,  or  else 
only  the  general  free  surfaces  develop  walls. 
It  is  in  the  nature  of  this  almost  universal  in- 
vestment that  it  is  proposed  to  point  out  a 
fundamental  distinction  between  animals  and 
plants. 

In  attempting  to  distinguish  animals  and 
plants  by  means  of  definite  characters,  there 
is,  however,  another  point  that  first  needs 
attention.  Diagnostic  characters  can  only  be 
drawn  between  like  things,  and  in  so  far  as 
the  characters  are  also  fundamental  they 
must  be  based  upon  fundamental  features.  In 
searching  for  essential  points  of  resemblance 
or  dissimilarity,  it  cannot  be  denied  that  the 
normal   individual   in   possession    of  its  full 


LIVING   PLANTS 


Characters  to  be 
taken  from  the 
active  organism 


Reproductive 
states  to  be 
ignored 


Animals  and 
plants  defined 


powers  is  the  real  and  genuine  organism  to 
which  attention  is  to  be  directed.  Secondary 
characters  may  be  drawn  from  adaptive  and 
more  or  less  incidental  structures,  but  not  so 
the  primary  ones.  Of  all  adaptive  or  ecolo- 
gical features  of  the  organism  the  reproduc- 
tive organs  and  processes  are  most  prominent, 
and  have  naturally  attracted  great  attention. 
Botany  has  been  popularly  styled  the  study 
of  flowers,  although  flowers  are  only  the  dec- 
orated vestibule  to  the  real  sanctuary  of  the 
science.  In  trying  to  discover  the  innermost 
reasons  for  establishing  a  criterion  between 
the  two  great  classes  of  beings,  only  the  nor- 
mal vegetative  state  of  organisms  need,  there- 
fore,be  considered,  and  the  reproductive  state, 
when  the  organism  disports  as  a  new-born 
entity  of  naked  protoplasm,  or  is  reduced  to 
a  spore  or  an  egg,  or  hibernates  in  seed  or 
cyst  with  protective  and  dispersive  append- 
ages, may  be  ignored.  We  are  to  keep  in  view 
only  the  vegetative  organism,  and  not  the 
mode  in  which  a  succession  of  individuals  is 
maintained. 

The  fundamental  characters  of  animals  and 
plants  may,  in  accordance  with  what  has 
been  said,  be  given  as  follows : 

Plants  are  organisms  possessing  a  carho- 
hydrous  investment. 


PLANTS  AND  ANIMALS 


Animals  are  organisms  possessing  a  nitro- 
genous investment. 

These  characters  hold  good  for  the  active 
individual  only,  and  have  no  necessary  appli- 
cation to  reproductive  stages.  They  are  diag- 
nostic characters  and  are  not  to  be  considered 
as  in  anywise  defining  the  powers  or  func- 
tions of  the  two  classes. 

In  cellular  organisms  the  investment  may 
extend  to  each  protoplasmic  unit,  as  is  usual 
in  plants,  or  to  the  units  of  certain  tissues,  as 
is  usual  in  animals,  or  be  developed  only  upon 
the  general  exterior,  as  is  specially  the  case  in 
coenocytic  organisms,  like  some  of  the  com- 
mon molds  and  sea-weeds  {Mucorinse  and 
Siphonaceas) . 

By  designating  the  constitution  of  the  pro- 
tective investment,  it  is  intended  to  cover 
only  the  original  or  basic  substance  of  which 
it  is  composed,  without  reference  to  subse- 
quent depositions  or  infiltrations,  of  what- 
ever character  they  may  be.  Thus  in  the 
walls  of  grasses  and  Equiseti  there  is  often  a 
great  amount  of  silica,  in  certain  seaweeds 
(Corallina)  much  lime,  in  tunicates  so  much 
cellulose  that  it  sometimes  amounts  to  one- 
fourth  of  the  dry  weight,  and  yet,  in  the  case 
of  the  plants  named,  the  original  and  funda- 


LIVING  PLANTS 


Physical 
features  of 
cell  walls 


mental  substance  of  the  wall  iscarbohydrous, 
and  in  the  animals  nitrogenous. 

The  carbohydrous  investment  of  organisms, 
chemically  considered,  is  probably  always 
some  form  of  cellulose.  There  are  primary 
and  compound  celluloses,  and  various  modifi- 
cations of  these.  In  some  instances  nitrogen 
seems  to  be  associated  with  the  cellulose,  as 
Winterstein  has  recently  claimed  in  the  case 
of  certain  fungi,  but  of  the  nature  of  this  asso- 
ciation nothing  is  definitely  known  ;  the  facts 
can  have  little  bearing  ui3on  the  fundamental 
proposition  here  laid  down. 

The  nitrogenous  investment  is  chemically 
always  of  the  nature  of  a  non-protoplasmic 
proteid,  of  very  complex  molecular  structure, 
undoubtedly  varying  much  in  different  organ- 
isms. 

Both  the  carboh3alrous  and  nitrogenous 
vestural  substances  are  very  likely  chemically 
analogous,  as  maintained  by  Elsberg  some 
fifteen  years  ago.  Quite  recently  Cross  and 
Bevan  in  their  treatise  on  cellulose  suggested 
that  the  substance  of  the  proteid  cell  wall 
"may  prove  to  be  of  similar  carbon  configur- 
ation to  that  of  cellulose." 

But  in  physical  characters  the  two  kinds  of 
cell  investiture  are  widely  different,  and  espec- 
ially so  in  their  degree  of  elasticity.      Carbo- 


PLANTS  AND  ANIMALvS 


hydrous  membranes  stretch  but  little,  while 
nitrogenous  membranes  are  highly  extensible; 
and  herein  lies  the  basis  of  the  wonderful  di- 
vergence in  mobility  shown  by  animals  and 
plants.  The  power  of  free  movement,  which 
characterizes  the  animal  and  has  rendered 
possible  its  great  and  varied  development, 
depends  primarily  upon  the  nature  of  the  in- 
vestment, just  as  the  rigidity  of  plant  bodies 
and  their  slow  adjustments  also  depend  by 
restriction  upon  the  investment.  It  is  no 
doubt  possible  in  ultimate  analysis  to  trace 
many  of  the 
prominent  phy- 
siological char- 
acters of  both 
kingdoms  to 
this  difference 
in  structure. 

In  applying 
the  crucial  test, 
some  organ- 
isms present 
special  difficult- 
ies. Some  forms 
in  their  vegeta- 
tive state  con- 
sist of  so-called 
naked  protoplasm,  of  which  themostcon 


# 


-:> 


Fig.  25. — A  mycetozoan  in  its 
tive  or  plasmodial  state,  much 
fied.     (After  Cienkowski.) 


egeta- 
nagui- 


Thc  test 
applied 


l.IVING  PLANTS 


uous  and  well- 
known  examples 
are  the  mycetozo- 
ans.  Many  spe- 
cies of  these  fun- 
g  US-animals 

Fig.  26.— A  niTcetozoan   {Dictyrli-  (   -t^  1  '  Z  6  til  16  re) 

urn    cernuum)    in    its   resting   state,  pOSSeSS     a    ciis- 

showing  four  fruiting  stalks  attached  .                             . 

to  a  piece  of  bark.     Enlarged  ten  di-  t  1  n  C  t           nitrOg- 

ameters.    (After  Engler  and  Prantl. )  enOUS       envclope 

about  the  p 1  a  s  m  o  d  i  u  m , 
w^hich  b^^  its  chemical  reac- 
tion is  shown  to  be  non- 
protoplasmic,  and  it  may 
be  inferred  that  careful  ex- 
amination will  find  it  pres- 
ent in  most  of  the  species, 
and  that  it  can  be  considered 
as  potential  or  undeveloped 
in  the  others.  The_v  are, 
therefore,  distincth^  animal 
in  their  fundamental  char- 
acteristic. Although  usu- 
ally treated  in  botanical 
text-books  and  studied  by 
botanists,  they  were  shown 
by  DeBary,  as  long  ago  as 

1864,    to    have    more   points  stalk  from  above.     En- 
P  j_         -J.!  •  1      larged    fiftT    diameters. 

of  agreement  with  animals  ^_^,^^^.jj^g-^^^^p^^^„,,., 


One  fruiting 


PLANTS  AND  ANIMALS 


than  with  plants,  and  he  beheved  them  to  be 
"outside  the  hmitsof  the  vegetable  kingdom." 
This  separation  by  DeBary  was  made  without 
reference  to  a  nitrogenous  membrane,  which 
may,  however,  be  considered  the  crucial  diag- 
nostic character. 

Another  set  of  organisms,  with  apparently 
naked  protoplasm  during  the  vegetative 
stage,  are  the  endophytic  parasites  belonging 
to  the  group 
of  genera 
represented 
by  Synchyt- 
rium,  Woro- 
nina,  Olpidi- 
opsis,  Rozel- 
la  and  Rees- 
ia.    Whether 

thev        ever      ^*^-    ^^- — ^^    amcEba    (Amosbn  pruteus). 
The  clear  spot  is  a  pulsating  vacuole.    Greatlv 
possess     any  enlarged.      (After  Leidy.) 

demonstrable  nitrogenous  envelope  has  not 
been  ascertained,  but  it  is  known  with  much 
certainty  that  they  have  no  cellulose  envelope; 
they  are,  therefore,  not  plants,  and  must,  in 
consequence,  be  animals.  This  disposition  of 
them  has  already  been  made  by  Zopf  on  the 
ground  that  a  "plasmodial  character  of  the 
vegetative  condition  is  entirely  foreign  to  the 
Eumycetes."      The  Chytridiacege,  which   are 


LIVING  PLANTS 


usually  associated  with  the  Synchytria,  have 
a  much  reduced  but  demonstrable  mycelium 
formed  of  cellulose,  and  are,  therefore,  unmis- 
takable plants. 

Among  the  lowest  forms,  as  generally  clas- 
sified, the  Rhizopods,  including  Amoeba,  and 
the  far  simpler  Monera,  show  no  distinct  en- 
velope, either  nitrogenous  or  carbohydrous, 
but  as  the  other  affinities  appear  to  be  with 
animals  rather  than  with  plants,  they  are 
doubtless  rightly  placed  in  the  animal  king- 
dom. It  is  reasonable  to  expect  that  more 
careful  examination  will,  in  some  cases,  show 
a  simple  or  imperfectly  formed  nitrogenous 
envelope. 

The  crucial  diagnostic  character,  which  is 
here  proposed,  has  in  its  favor  the  separation 
of  plants  and  animals  upon  a  line  which  ac- 
cords well  with  the  consensus  of  opinion  of 
thoughtful  students,  both  botanists  and  zo- 
ologists, an  opinion  which  has  been  formed 
from  a  variety  of  structural,  physiological  and 
developmental  data.  Full  relationship  must 
necessarily  be  adduced  from  a  study  of  the  life- 
history  of  organisms;  diagnostic  characters 
only  form  points  of  departure. 


INDEX  TO  PLANT  NAMES 


INDEX  TO  PLANT  NAMES. 

ACANTHUS 92 

Acer  (maple) 182 

Ailanthus 163 

Alder 181 

AlgjE 175,184,  185,  190,191 

Alnus  (alder) 182 

Aloe 187 

Alpina 182 

Amaranth 171 

Ampelopsis 171 

Anthurium 188 

Arisaema  triphyllum 123,  126,  127,  129,  131,  133 

134,  138,  139,  141 

Aroids 89 

Asparagus 100 

Aspen 7 

Avena  (oats) 24 

BACILLUS   BRUNNEUS 176 

Bacillus  cinnabareus 176 

Bacteria 103,  104,  152,  175,  184,  190,  200,  201 

Bacterium  photometricum 177 

"  -viride 177 

Banana 182 

Barley 108 

Basil 92 

Bean 11,  55,  100,  107,  108,  201 

Beech 197 

Begonia 188,  189 

falcata 187,  189 

"       imperialis 187 

Belemcanda 182 

Bircti 161 

Bladderwort  (Utriciilaria) 96 

Blight 200 

Burdock 196 


LIVING   PLANTS 


CABBAGE 100,  108 

Calla  palustris 135,  138 

Canna 179 

Carpinus  (water  beech) 182 

Carrot 176 

Cassia 48,  55 

"      ChamEecrista 48 

"      nictitans 48 

Cauliflower 108 

Cercis  Canadensis  (redbud) 15 

Charlock  {Brassica  Sinapisirum)  14 

Chytridiaceae 225 

Cissus 1  88 

Cnicvis  discolor  (thistle) 189 

Cocklebur  (Xanthium) 40 

Coffee 201 

Coleus 92 

Compass  plants 42,  44,  46 

Conifers 84 

Corallina 221 

Corn  iZea  mais) 102,  108  109  110,  119,  201 

Corylus   (hazel) 182 

Cotton  rust 103 

DATE 136 

Dentaria  bulbifera 181 

Dionoea  muscipula 4,  188 

Duckweed 173,  174 

EGG  PLANT 100 

Elodea  Canadensis 96,  181 

Equisetum 221 

Eranthemum 186 

Eumycctes 225 

Euphorbiaceae 48 

FERNS 205 

Fraxinus  (ash) 182 

Fuchsia  triphyll  a 186 

Fungi 147,  175,  175,  190.200 

GERANIUM 170,  188 

H.BM  ATOCOCCUS 185 

Haematoxylon 192 

Hawthorne  {Cratwgus) 162 


Hibiscus  rosa-sinensis 138 

Horse  chestnut  {^^sciilus) 163 

Horseweed  (Ambrosia  trifida) 40 

IRIS 205 

Isopyrum  biternatum 138 

JIMSONWEED,  {Datura  Strnmonium) 40 

Juniper 94 

Justitia 13S 

I.ACTUCA    LUDOVICIANA 46 

Lactuca  sativa 31 

Scariola 31 

Leaf-mildew / 75 

Leguminosae 47,  60 

Lemna  trisulca 173 

Lettuce 31,  38,  46,  100 

Lichens 85 

Lilium  stiperbum 138 

Linden  (Tilia  Americana) 81 

Liverworts 85 

Locust  {Robinia  Pseudacacia) 55,  62,  81 

Logwood 192 

MALVACE^ 47 

Mandrake 64,65 

Mangif  era 181 

Mango  ( Mangifera  ) 181 

Maple 161 

Marantacere 48 

M aranta  zebrina 189 

Marguerite  (Leucanthemum) 41 

Marsiliacew 47 

Melon 92,  159 

Mertensia 177 

Micrococcus  agilis 176 

Mildew 200 

Mimosa  pudica 17,  47,  48,  182 

Molds 147,  200,  221 

Mosses 84 

Mucorineae 217,  221 

Musa 182 

Mushrooms 147 

OAK  (Quercus) 161,  181,  197 

Oats  {Avena  sativa) 108,  113,  114,  120 


LIVING  PLANTS 


Olpidiopsis 225 

Onion 108 

Ostrya  (ironwood) 182 

Oxalidse 47 

Oxalis 55 

"     Acetosella 189 

"     floribunda 138 

"     vespertilionis 138 

Ox-eye  daisy  (Leucanthemiun) 41 

PEAS 100,  107,   108,  109,111,113,118,119 

Peach  yellows 103 

Phalaris 24 

Philotria  Canadensis 96,  181 

Phoenix  dactylifera  (date) 136,  138 

Pigweed  CAmaranthiis  retroflexiis) 40 

Pine 94 

Pinus  huniilis 94 

Piper  porphyraceum 187 

Platanns  (Sycamore) 181 

Poison  oak  (Rlnis  toxicodendron) 162 

Pondweed  (Elodea) 96,  181 

Poplar 157 

Populus 182 

Potato 201 

Prickly  lettuce 31,  33,  43 

Pultnonaria 177 

Pumpkin  {Cucurhita  Pepo) 74 

Purslane  (Portulaca  oleracea) .40,  196 

RADISH 100 

Ragw^eed  {Ambrosia  artemisiee folia) 40 

Ranunculus  ficarioides 186,  187 

Redbud  (Cercis) 15,  81 

Red  maple 185 

Red  sea- weed 185 

Reesia 225 

Rhododendron 94 

Robinia  Pseudacacia 62 

Rosin  weed  {Silphium  laciniatum) 43 

Rots 200 

Rozella 225 

Rumex  (dock) 182 

Rusts 200 

Rye 108 


INDEX 


SALIX   (willow) 182 

Salmon-fungus 75 

Saprolegnia 75 

Sarcis a  rosea 177 

Satureja  hortensis 180 

Sea- weeds 221 

Sensitive  plant 17,  47.  4-8,  68,  81,  182 

Shame  weed 48 

Shepherd's  purse 196 

Silphium  laciniatum 43,  46 

Siphonacea: 211 

Slime-mold 75 

Spirogyra ,     91 

Stonewort  (Chara^ 96 

Sumac  {Rhus  glabra) 162 

Summer  savory 180 

Sundew 7,  193 

Symphytum 177 

Synchytrium 225,  226 

THISTLES  (Cnicus) 40 

Tiger  lily 207 

Toadstools 147 

Tobacco 92,  159 

Tomato 100,  201 

Tradescantia 18S 

Trillium  erectum 138 

Trillium  erythrocarpum 138 

Tulip  tree  (Liriodendron  tiilipifera) 162 

Turnip 108 

ULMUS  (elm) 182 

Uncaria  alpina 182 

Utricularia 96 

Utricularia  vulgaris 181 

VENUS  FLY-TRAP 4,  61 

Vines  (Vitis) 162,  163 

Virginia  creeper  (Ampelopsis) 163,  191 

WATER  LILY  (Nymphwa) 95 

Water-weed  lElodea  Canadensis) 74 

Wheat....  102,  103,  104,  106,  108,  109,  114,  116,  119,  201 

Wild  cucumber  (Echinocystis  lohata) 67 

Wild  lettuce 30,  31,  35,  41 

Wild  sensitive  plant 48 

Willow  (Salix) 177 


234  LIVING   PLANTS 

Woronina 225 

YEAST 201 

ZEA  MAIS  (corn) 135,  138 


Jf.  C.  State  Collef« 


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North  Carolina  State  University  Libraries 

QK81  .A7 

LIVING  PLANTS  AND  THEIR  PROPERTIES  A  COLLECTI 


S02776955  Q 


